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/*
* Copyright 2022 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "src/gpu/graphite/render/AnalyticRRectRenderStep.h"
#include "src/base/SkVx.h"
#include "src/core/SkRRectPriv.h"
#include "src/gpu/graphite/DrawParams.h"
#include "src/gpu/graphite/DrawWriter.h"
#include "src/gpu/graphite/render/CommonDepthStencilSettings.h"
// This RenderStep is flexible and can draw filled rectangles, filled quadrilaterals with per-edge
// AA, filled rounded rectangles with arbitrary corner radii, stroked rectangles with any join,
// and stroked rounded rectangles with circular corners (each corner can be different or square).
// We combine all of these together to maximize batching across simple geometric draws and reduce
// the number pipeline specializations. Additionally, these primitives are the most common
// operations and help us avoid triggering MSAA.
//
// Each of these "primitives" is represented by a single instance. The instance attributes are
// flexible enough to describe any of the above shapes without relying on uniforms to define its
// operation. The attributes encode shape as follows:
//
// float4 xRadiiOrFlags - if any components is > 0, the instance represents a filled round rect
// with elliptical corners and these values specify the X radii in top-left CW order.
// Otherwise, if .x < -1, the instance represents a stroked or hairline [round] rect, where .y
// differentiates hairline vs. stroke. If .y is negative, then it is a hairline and xRadiiOrFlags
// stores (-2 - X radii); otherwise it is a regular stroke and .z holds the stroke radius and
// .w stores the join limit (matching StrokeStyle's conventions).
// Else it's a filled quadrilateral with per-edge AA defined by each component: aa != 0.
// float4 radiiOrQuadXs - if in filled round rect or hairline [round] rect mode, these values
// provide the Y radii in top-left CW order. If in stroked [round] rect mode, these values
// provide the circular corner radii (same order). Otherwise, when in per-edge quad mode, these
// values provide the X coordinates of the quadrilateral (same order).
// float4 ltrbOrQuadYs - if in filled round rect mode or stroked [round] rect mode, these values
// define the LTRB edge coordinates of the rectangle surrounding the round rect (or the
// rect itself when the radii are 0s). Otherwise, in per-edge quad mode, these values provide
// the Y coordinates of the quadrilateral.
//
// From the other direction, shapes produce instance values like:
// - filled rect: [-1 -1 -1 -1] [L R R L] [T T B B]
// - stroked rect: [-2 0 stroke join] [0 0 0 0] [L T R B]
// - hairline rect: [-2 -2 -2 -2] [0 0 0 0] [L T R B]
// - filled rrect: [xRadii(tl,tr,br,bl)] [yRadii(tl,tr,br,bl)] [L T R B]
// - stroked rrect: [-2 0 stroke join] [radii(tl,tr,br,bl)] [L T R B]
// - hairline rrect: [-2-xRadii(tl,tr,br,bl)] [radii(tl,tr,br,bl)] [L T R B]
// - per-edge quad: [aa(t,r,b,l) ? -1 : 0] [xs(tl,tr,br,bl)] [ys(tl,tr,br,bl)]
//
// This encoding relies on the fact that a valid SkRRect with all x radii equal to 0 must have
// y radii equal to 0 (so it's a rectangle and we can treat it as a quadrilateral with
// all edges AA'ed). This avoids other encodings' inability to represent a quad with all edges
// anti-aliased (e.g. checking for negatives in xRadiiOrFlags to turn on per-edge mode).
//
// From this encoding, data can be unpacked for each corner, which are equivalent under
// rotational symmetry. A corner can have an outer curve, be mitered, or be beveled. It can
// have an inner curve, an inner miter, or fill the interior. Per-edge quads are always mitered
// and fill the interior, but the vertices are placed such that the edge coverage ramps can
// collapse to 0 area on non-AA edges.
//
// The vertices that describe each corner are placed so that edges, miters, and bevels calculate
// coverage by interpolating a varying and then clamping in the fragment shader. Triangles that
// cover the inner and outer curves calculate distance to the curve within the fragment shader.
//
// See https://docs.google.com/presentation/d/1MCPstNsSlDBhR8CrsJo0r-cZNbu-sEJEvU9W94GOJoY/edit?usp=sharing
// for diagrams and explanation of how the geometry is defined.
//
// AnalyticRRectRenderStep uses the common technique of approximating distance to the level set by
// one expansion of the Taylor's series for the level set's equation. Given a level set function
// C(x,y), this amounts to calculating C(px,py)/|∇C(px,py)|. For the straight edges the level set
// is linear and calculated in the vertex shader and then interpolated exactly over the rectangle.
// This provides distances to all four exterior edges within the fragment shader and allows it to
// reconstruct a relative position per elliptical corner. Unfortunately this requires the fragment
// shader to calculate the length of the gradient for straight edges instead of interpolating
// exact device-space distance.
//
// All four corner radii are potentially evaluated by the fragment shader although each corner's
// coverage is only calculated when the pixel is within the bounding box of its quadrant. For fills
// and simple strokes it's theoretically valid to have each pixel calculate a single corner's
// coverage that was controlled via the vertex shader. However, testing all four corners is
// necessary in order to correctly handle self-intersecting stroke interiors. Similarly, all four
// edges must be evaluated in order to handle extremely thin shapes; whereas often you could get
// away with tracking a single edge distance per pixel.
//
// Analytic derivatives are used so that a single pipeline can be used regardless of HW derivative
// support or for geometry that would prove difficult for forward differencing. The device-space
// gradient for ellipses is calculated per-pixel by transforming a per-pixel local gradient vector
// with the Jacobian of the inverse local-to-device transform:
//
// (px,py) is the projected point of (u,v) transformed by a 3x3 matrix, M:
// [x(u,v) / w(u,v)] [x] [m00 m01 m02] [u]
// (px,py) = [y(u,v) / w(u,v)] where [y] = [m10 m11 m12]X[v] = M*(u,v,1)
// [w] [m20 m21 m22] [1]
//
// C(px,py) can be defined in terms of a local Cl(u,v) as C(px,py) = Cl(p^-1(px,py)), where p^-1 =
//
// [x'(px,py) / w'(px,py)] [x'] [m00' m01' * m02'] [px]
// (u,v) = [y'(px,py) / w'(px,py)] where [y'] = [m10' m11' * m12']X[py] = M^-1*(px,py,0,1)
// [w'] [m20' m21' * m22'] [ 1]
//
// Note that if the 3x3 M was arrived by dropping the 3rd row and column from a 4x4 since we assume
// a local 3rd coordinate of 0, M^-1 is not equal to the 4x4 inverse with dropped rows and columns.
//
// Using the chain rule, then ∇C(px,py)
// = ∇Cl(u,v)X[1/w'(px,py) 0 -x'(px,py)/w'(px,py)^2] [m00' m01']
// [ 0 1/w'(px,py) -y'(px,py)/w'(px,py)^2]X[m10' m11']
// [m20' m21']
//
// = 1/w'(px,py)*∇Cl(u,v)X[1 0 -x'(px,py)/w'(px,py)] [m00' m01']
// [0 1 -y'(px,py)/w'(px,py)]X[m10' m11']
// [m20' m21']
//
// = w(u,v)*∇Cl(u,v)X[1 0 0 -u] [m00' m01']
// [0 1 0 -v]X[m10' m11']
// [m20' m21']
//
// = w(u,v)*∇Cl(u,v)X[m00'-m20'u m01'-m21'u]
// [m10'-m20'v m11'-m21'v]
//
// The vertex shader calculates the rightmost 2x2 matrix and interpolates it across the shape since
// each component is linear in (u,v). ∇Cl(u,v) is evaluated per pixel in the fragment shader and
// depends on which corner and edge being evaluated. w(u,v) is the device-space W coordinate, so
// its reciprocal is provided in sk_FragCoord.w.
namespace skgpu::graphite {
using AAFlags = EdgeAAQuad::Flags;
static skvx::float4 load_x_radii(const SkRRect& rrect) {
return skvx::float4{rrect.radii(SkRRect::kUpperLeft_Corner).fX,
rrect.radii(SkRRect::kUpperRight_Corner).fX,
rrect.radii(SkRRect::kLowerRight_Corner).fX,
rrect.radii(SkRRect::kLowerLeft_Corner).fX};
}
static skvx::float4 load_y_radii(const SkRRect& rrect) {
return skvx::float4{rrect.radii(SkRRect::kUpperLeft_Corner).fY,
rrect.radii(SkRRect::kUpperRight_Corner).fY,
rrect.radii(SkRRect::kLowerRight_Corner).fY,
rrect.radii(SkRRect::kLowerLeft_Corner).fY};
}
static float local_aa_radius(const Transform& t, const SkV2& p) {
// TODO: This should be the logic for Transform::scaleFactor()
// [m00 m01 * m03] [f(u,v)]
// Assuming M = [m10 m11 * m13], define the projected p'(u,v) = [g(u,v)] where
// [ * * * * ]
// [m30 m31 * m33]
// [x] [u]
// f(u,v) = x(u,v) / w(u,v), g(u,v) = y(u,v) / w(u,v) and [y] = M*[v]
// [*] = [0]
// [w] [1]
//
// x(u,v) = m00*u + m01*v + m03
// y(u,v) = m10*u + m11*v + m13
// w(u,v) = m30*u + m31*v + m33
//
// dx/du = m00, dx/dv = m01,
// dy/du = m10, dy/dv = m11
// dw/du = m30, dw/dv = m31
//
// df/du = (dx/du*w - x*dw/du)/w^2 = (m00*w - m30*x)/w^2 = (m00 - m30*f)/w
// df/dv = (dx/dv*w - x*dw/dv)/w^2 = (m01*w - m31*x)/w^2 = (m01 - m31*f)/w
// dg/du = (dy/du*w - y*dw/du)/w^2 = (m10*w - m30*y)/w^2 = (m10 - m30*g)/w
// dg/dv = (dy/dv*w - y*dw/du)/w^2 = (m11*w - m31*y)/w^2 = (m11 - m31*g)/w
//
// Singular values of [df/du df/dv] define perspective correct minimum and maximum scale factors
// [dg/du dg/dv]
// for M evaluated at (u,v)
const SkM44& matrix = t.matrix();
SkV4 devP = matrix.map(p.x, p.y, 0.f, 1.f);
const float dxdu = matrix.rc(0,0);
const float dxdv = matrix.rc(0,1);
const float dydu = matrix.rc(1,0);
const float dydv = matrix.rc(1,1);
const float dwdu = matrix.rc(3,0);
const float dwdv = matrix.rc(3,1);
float invW2 = sk_ieee_float_divide(1.f, (devP.w * devP.w));
// non-persp has invW2 = 1, devP.w = 1, dwdu = 0, dwdv = 0
float dfdu = (devP.w*dxdu - devP.x*dwdu) * invW2; // non-persp -> dxdu -> m00
float dfdv = (devP.w*dxdv - devP.x*dwdv) * invW2; // non-persp -> dxdv -> m01
float dgdu = (devP.w*dydu - devP.y*dwdu) * invW2; // non-persp -> dydu -> m10
float dgdv = (devP.w*dydv - devP.y*dwdv) * invW2; // non-persp -> dydv -> m11
// no-persp, these are the singular values of [m00,m01][m10,m11], which is just the upper 2x2
// and equivalent to SkMatrix::getMinmaxScales().
float s1 = dfdu*dfdu + dfdv*dfdv + dgdu*dgdu + dgdv*dgdv;
float e = dfdu*dfdu + dfdv*dfdv - dgdu*dgdu - dgdv*dgdv;
float f = dfdu*dgdu + dfdv*dgdv;
float s2 = SkScalarSqrt(e*e + 4*f*f);
float singular1 = SkScalarSqrt(0.5f * (s1 + s2));
float singular2 = SkScalarSqrt(0.5f * (s1 - s2));
// singular1 and 2 represent the minimum and maximum scale factors at that transformed point.
// Moving 1 from 'p' before transforming will move at least minimum and at most maximum from
// the transformed point. Thus moving between [1/max, 1/min] pre-transformation means post
// transformation moves between [1,max/min] so using 1/min as the local AA radius ensures that
// the post-transformed point is at least 1px away from the original.
float aaRadius = sk_ieee_float_divide(1.f, std::min(singular1, singular2));
if (sk_float_isfinite(aaRadius)) {
return aaRadius;
} else {
// Treat NaNs and infinities as +inf, which will always trigger the inset self-intersection
// logic that snaps inner vertices to the center instead of insetting by the local AA radius
return SK_FloatInfinity;
}
}
static float local_aa_radius(const Transform& t, const Rect& bounds) {
// Use the maximum radius of the 4 corners so that every local vertex uses the same offset
// even if it's more conservative on some corners (when the min/max scale isn't constant due
// to perspective).
if (t.type() < Transform::Type::kProjection) {
// Scale factors are constant, so the point doesn't really matter
return local_aa_radius(t, SkV2{0.f, 0.f});
} else {
// TODO can we share calculation here?
float tl = local_aa_radius(t, SkV2{bounds.left(), bounds.top()});
float tr = local_aa_radius(t, SkV2{bounds.right(), bounds.top()});
float br = local_aa_radius(t, SkV2{bounds.right(), bounds.bot()});
float bl = local_aa_radius(t, SkV2{bounds.left(), bounds.bot()});
return std::max(std::max(tl, tr), std::max(bl, br));
}
}
static bool opposite_insets_intersect(const SkRRect& rrect, float strokeRadius, float aaRadius) {
// One AA inset per side
const float maxInset = strokeRadius + 2.f * aaRadius;
return // Horizontal insets would intersect opposite corner's curve
maxInset >= rrect.width() - rrect.radii(SkRRect::kLowerLeft_Corner).fX ||
maxInset >= rrect.width() - rrect.radii(SkRRect::kLowerRight_Corner).fX ||
maxInset >= rrect.width() - rrect.radii(SkRRect::kUpperLeft_Corner).fX ||
maxInset >= rrect.width() - rrect.radii(SkRRect::kUpperRight_Corner).fX ||
// Vertical insets would intersect opposite corner's curve
maxInset >= rrect.height() - rrect.radii(SkRRect::kLowerLeft_Corner).fY ||
maxInset >= rrect.height() - rrect.radii(SkRRect::kLowerRight_Corner).fY ||
maxInset >= rrect.height() - rrect.radii(SkRRect::kUpperLeft_Corner).fY ||
maxInset >= rrect.height() - rrect.radii(SkRRect::kUpperRight_Corner).fY;
}
static bool opposite_insets_intersect(const Geometry& geometry,
float strokeRadius,
float aaRadius) {
if (geometry.isEdgeAAQuad()) {
SkASSERT(strokeRadius == 0.f);
const EdgeAAQuad& quad = geometry.edgeAAQuad();
if (quad.edgeFlags() == AAFlags::kNone) {
// If all edges are non-AA, there won't be any insetting.
return false;
} else if (quad.isRect()) {
auto inset = skvx::float2(quad.edgeFlags() & AAFlags::kLeft ? aaRadius : 0.f,
quad.edgeFlags() & AAFlags::kTop ? aaRadius : 0.f) +
skvx::float2(quad.edgeFlags() & AAFlags::kRight ? aaRadius : 0.f,
quad.edgeFlags() & AAFlags::kBottom ? aaRadius : 0.f);
return any(quad.bounds().size() <= inset);
} else {
// For simplicity an arbitrary quadrilateral with any AA assumes the insets intersect.
return true;
}
} else {
const Shape& shape = geometry.shape();
if (shape.isRect()) {
return any(shape.rect().size() <= 2.f * (strokeRadius + aaRadius));
} else {
SkASSERT(shape.isRRect());
return opposite_insets_intersect(shape.rrect(), strokeRadius, aaRadius);
}
}
}
// Represents the per-vertex attributes used in each instance.
struct Vertex {
SkV2 fPosition;
SkV2 fNormal;
float fNormalScale;
float fCenterWeight;
};
// Allowed values for the center weight instance value (selected at record time based on style
// and transform), and are defined such that when (insance-weight > vertex-weight) is true, the
// vertex should be snapped to the center instead of its regular calculation.
static constexpr float kSolidInterior = 1.f;
static constexpr float kStrokeInterior = 0.f;
static constexpr float kFilledStrokeInterior = -1.f;
// Special value for local AA radius to signal when the self-intersections of a stroke interior
// need extra calculations in the vertex shader.
static constexpr float kComplexAAInsets = -1.f;
static constexpr int kCornerVertexCount = 9; // sk_VertexID is divided by this in SkSL
static constexpr int kVertexCount = 4 * kCornerVertexCount;
static constexpr int kIndexCount = 69;
static void write_index_buffer(VertexWriter writer) {
static constexpr uint16_t kTL = 0 * kCornerVertexCount;
static constexpr uint16_t kTR = 1 * kCornerVertexCount;
static constexpr uint16_t kBR = 2 * kCornerVertexCount;
static constexpr uint16_t kBL = 3 * kCornerVertexCount;
static const uint16_t kIndices[kIndexCount] = {
// Exterior AA ramp outset
kTL+0,kTL+4,kTL+1,kTL+5,kTL+2,kTL+3,kTL+5,
kTR+0,kTR+4,kTR+1,kTR+5,kTR+2,kTR+3,kTR+5,
kBR+0,kBR+4,kBR+1,kBR+5,kBR+2,kBR+3,kBR+5,
kBL+0,kBL+4,kBL+1,kBL+5,kBL+2,kBL+3,kBL+5,
kTL+0,kTL+4, // close and jump to next strip
// Outer to inner edges
kTL+4,kTL+6,kTL+5,kTL+7,
kTR+4,kTR+6,kTR+5,kTR+7,
kBR+4,kBR+6,kBR+5,kBR+7,
kBL+4,kBL+6,kBL+5,kBL+7,
kTL+4,kTL+6, // close and jump to next strip
// Fill triangles
kTL+6,kTL+8,kTL+7, kTL+7,kTR+8,
kTR+6,kTR+8,kTR+7, kTR+7,kBR+8,
kBR+6,kBR+8,kBR+7, kBR+7,kBL+8,
kBL+6,kBL+8,kBL+7, kBL+7,kTL+8,
kTL+6 // close
};
writer << kIndices;
}
static void write_vertex_buffer(VertexWriter writer) {
// Allowed values for the normal scale attribute. +1 signals a device-space outset along the
// normal away from the outer edge of the stroke. 0 signals no outset, but placed on the outer
// edge of the stroke. -1 signals a local inset along the normal from the inner edge.
static constexpr float kOutset = 1.0;
static constexpr float kInset = -1.0;
static constexpr float kCenter = 1.f; // "true" as a float
// Zero, but named this way to help call out non-zero parameters.
static constexpr float _______ = 0.f;
static constexpr float kHR2 = 0.5f * SK_FloatSqrt2; // "half root 2"
// This template is repeated 4 times in the vertex buffer, for each of the four corners.
// The vertex ID is used to lookup per-corner instance properties such as corner radii or
// positions, but otherwise this vertex data produces a consistent clockwise mesh from
// TL -> TR -> BR -> BL.
static constexpr Vertex kVertexTemplate[kVertexCount] = {
// ** TL **
// Device-space AA outsets from outer curve
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kOutset, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kOutset, _______ },
// Outer anchors (no local or device-space normal outset)
{ {1.0f, 0.0f}, {kHR2, kHR2}, _______, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, _______, _______ },
// Inner curve (with additional AA inset in the common case)
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kInset, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kInset, _______ },
// Center filling vertices (equal to inner AA insets unless 'center' triggers a fill).
// TODO: On backends that support "cull" distances (and with SkSL support), these vertices
// and their corresponding triangles can be completely removed. The inset vertices can
// set their cull distance value to cause all filling triangles to be discarded or not
// depending on the instance's style.
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kInset, kCenter },
// ** TR **
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kOutset, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kOutset, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, _______, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, _______, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kInset, _______ },
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kInset, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kInset, kCenter },
// ** BR **
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kOutset, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kOutset, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, _______, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, _______, _______ },
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kInset, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kInset, _______ },
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kInset, kCenter },
// ** BL **
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kOutset, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, kOutset, _______ },
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kOutset, _______ },
{ {0.0f, 1.0f}, {kHR2, kHR2}, _______, _______ },
{ {1.0f, 0.0f}, {kHR2, kHR2}, _______, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kInset, _______ },
{ {1.0f, 0.0f}, {1.0f, 0.0f}, kInset, _______ },
{ {0.0f, 1.0f}, {0.0f, 1.0f}, kInset, kCenter },
};
writer << kVertexTemplate;
}
AnalyticRRectRenderStep::AnalyticRRectRenderStep(StaticBufferManager* bufferManager)
: RenderStep("AnalyticRRectRenderStep",
"",
Flags::kPerformsShading | Flags::kEmitsCoverage,
/*uniforms=*/{},
PrimitiveType::kTriangleStrip,
kDirectDepthGreaterPass,
/*vertexAttrs=*/{
{"position", VertexAttribType::kFloat2, SkSLType::kFloat2},
{"normal", VertexAttribType::kFloat2, SkSLType::kFloat2},
// TODO: These values are all +1/0/-1, or +1/0, so could be packed
// much more densely than as three floats.
{"normalScale", VertexAttribType::kFloat, SkSLType::kFloat},
{"centerWeight", VertexAttribType::kFloat, SkSLType::kFloat}
},
/*instanceAttrs=*/
{{"xRadiiOrFlags", VertexAttribType::kFloat4, SkSLType::kFloat4},
{"radiiOrQuadXs", VertexAttribType::kFloat4, SkSLType::kFloat4},
{"ltrbOrQuadYs", VertexAttribType::kFloat4, SkSLType::kFloat4},
// XY stores center of rrect in local coords. Z and W store values to
// control interior fill behavior. Z can be -1, 0, or 1:
// -1: A stroked interior where AA insets overlap, but isn't solid.
// 0: A stroked interior with no complications.
// 1: A solid interior (fill or sufficiently large stroke width).
// W specifies the size of the AA inset if it's >= 0, or signals that
// the inner curves intersect in a complex manner (rare).
{"center", VertexAttribType::kFloat4, SkSLType::kFloat4},
// TODO: pack depth and ssboIndex into 32-bits
{"depth", VertexAttribType::kFloat, SkSLType::kFloat},
{"ssboIndex", VertexAttribType::kInt, SkSLType::kInt},
{"mat0", VertexAttribType::kFloat3, SkSLType::kFloat3},
{"mat1", VertexAttribType::kFloat3, SkSLType::kFloat3},
{"mat2", VertexAttribType::kFloat3, SkSLType::kFloat3}},
/*varyings=*/{
// TODO: If the inverse transform is part of the draw's SSBO, we can
// reconstruct the Jacobian in the fragment shader using the existing
// local coordinates varying
{"jacobian", SkSLType::kFloat4}, // float2x2
// Distance to LTRB edges of unstroked shape. Depending on
// 'perPixelControl' these will either be local or device-space values.
{"edgeDistances", SkSLType::kFloat4}, // distance to LTRB edges
// TODO: These are constant for all fragments for a given instance,
// could we store them in the draw's SSBO?
{"xRadii", SkSLType::kFloat4},
{"yRadii", SkSLType::kFloat4},
// Matches the StrokeStyle struct (X is radius, Y < 0 is round join,
// Y = 0 is bevel, Y > 0 is miter join).
// TODO: These could easily be considered part of the draw's uniforms.
{"strokeParams", SkSLType::kFloat2},
// 'perPixelControl' is a tightly packed description of how to
// evaluate the possible edges that influence coverage in a pixel.
// The decision points and encoded values are spread across X and Y
// so that they are consistent regardless of whether or not MSAA is
// used and does not require centroid sampling.
//
// The signs of values are used to determine the type of coverage to
// calculate in the fragment shader and depending on the state, extra
// varying state is encoded in the fields:
// - A positive X value overrides all per-pixel coverage calculations
// and sets the pixel to full coverage. Y is ignored in this case.
// - A zero X value represents a solid interior shape.
// - X much less than 0 represents bidirectional coverage for a
// stroke, using a sufficiently negative value to avoid
// extrapolation from fill triangles. For actual shapes with
// bidirectional coverage, the fill triangles are zero area.
//
// - Y much greater than 0 takes precedence over the latter two X
// rules and signals that 'edgeDistances' holds device-space values
// and does not require additional per-pixel calculations. The
// coverage scale is encoded as (1+scale*w) and the bias is
// reconstructed from that. X is always 0 for non-fill triangles
// since device-space edge distance is only used for solid interiors
// - Otherwise, any negative Y value represents an additional
// reduction in coverage due to a device-space outset. It is clamped
// below 0 to avoid adding coverage from extrapolation.
{"perPixelControl", SkSLType::kFloat2},
}) {
// Initialize the static buffers we'll use when recording draw calls.
// NOTE: Each instance of this RenderStep gets its own copy of the data. Since there should only
// ever be one AnalyticRRectRenderStep at a time, this shouldn't be an issue.
write_vertex_buffer(bufferManager->getVertexWriter(sizeof(Vertex) * kVertexCount,
&fVertexBuffer));
write_index_buffer(bufferManager->getIndexWriter(sizeof(uint16_t) * kIndexCount,
&fIndexBuffer));
}
AnalyticRRectRenderStep::~AnalyticRRectRenderStep() {}
std::string AnalyticRRectRenderStep::vertexSkSL() const {
// TODO: Move this into a module
return R"(
const int kCornerVertexCount = 9; // KEEP IN SYNC WITH C++'s kCornerVertexCount
const float kMiterScale = 1.0;
const float kBevelScale = 0.0;
const float kRoundScale = 0.41421356237; // sqrt(2)-1
const float kEpsilon = 0.00024; // SK_ScalarNearlyZero
// Default to miter'ed vertex positioning. Corners with sufficiently large corner radii, or
// bevel'ed strokes will adjust vertex placement on a per corner basis. This will not affect
// the final coverage calculations in the fragment shader.
float joinScale = kMiterScale;
// Unpack instance-level state that determines the vertex placement and style of shape.
bool bidirectionalCoverage = center.z <= 0.0;
bool deviceSpaceDistances = false;
float4 xs, ys; // ordered TL, TR, BR, BL
if (xRadiiOrFlags.x < -1.0) {
// Stroked rect or round rect
xs = ltrbOrQuadYs.LRRL;
ys = ltrbOrQuadYs.TTBB;
if (xRadiiOrFlags.y < 0.0) {
// A hairline so the X radii are encoded as negative values in this field, and Y
// radii are stored directly in the subsequent float4.
xRadii = -xRadiiOrFlags - 2.0;
yRadii = radiiOrQuadXs;
// All hairlines use miter joins (join style > 0)
strokeParams = float2(0.0, 1.0);
} else {
xRadii = radiiOrQuadXs;
yRadii = xRadii; // regular strokes are circular
strokeParams = xRadiiOrFlags.zw;
if (strokeParams.y < 0.0) {
joinScale = kRoundScale; // the stroke radius rounds rectangular corners
} else if (strokeParams.y == 0.0) {
joinScale = kBevelScale;
} // else stay mitered
}
} else if (any(greaterThan(xRadiiOrFlags, float4(0.0)))) {
// Filled round rect
xs = ltrbOrQuadYs.LRRL;
ys = ltrbOrQuadYs.TTBB;
xRadii = xRadiiOrFlags;
yRadii = radiiOrQuadXs;
strokeParams = float2(0.0, -1.0); // A negative join style is "round"
} else {
// Per-edge quadrilateral, so we have to calculate the corner's basis from the
// quad's edges.
xs = radiiOrQuadXs;
ys = ltrbOrQuadYs;
xRadii = float4(0.0);
yRadii = float4(0.0);
strokeParams = float2(0.0, 1.0); // Will be ignored, but set to a "miter"
deviceSpaceDistances = true;
}
// Adjust state on a per-corner basis
int cornerID = sk_VertexID / kCornerVertexCount;
float strokeRadius = strokeParams.x; // alias
float2 cornerRadii = float2(xRadii[cornerID], yRadii[cornerID]);
float2 cornerAspectRatio = float2(1.0);
if (cornerRadii.x > kEpsilon && cornerRadii.y > kEpsilon) {
// Position vertices for an elliptical corner; overriding any previous join style since
// that only applies when radii are 0.
joinScale = kRoundScale;
cornerAspectRatio = cornerRadii.yx;
} else if (cornerRadii.x != 0 && cornerRadii.y != 0) {
// A very small rounded corner, which technically ignores style (i.e. should not be
// beveled or mitered), but place the vertices as a miter to fully cover it and let
// the fragment shader evaluate the curve per pixel.
joinScale = kMiterScale;
cornerAspectRatio = cornerRadii.yx;
} else if (strokeRadius > 0.0 && strokeRadius <= kEpsilon) {
// A stroked rectangular corner that could have a very small bevel or round join,
// so place vertices as a miter.
joinScale = kMiterScale;
}
float mirrorOffset = normalScale >= 0.0 ? 1.0 : 0.0;
if (joinScale == kMiterScale) {
mirrorOffset = 1.0;
cornerRadii = float2(0.0); // (will only affect vertex placement, not FS coverage)
}
// Calculate the local edge vectors, ordered L, T, R, B starting from the bottom left point.
// For quadrilaterals these are not necessarily axis-aligned, but in all cases they orient
// the +X/+Y normalized vertex template for each corner.
// TODO: Correct edge vectors for points, lines, and triangles.
float4 dx = xs - xs.wxyz;
float4 dy = ys - ys.wxyz;
float4 invEdgeLen = inversesqrt(dx*dx + dy*dy);
dx *= invEdgeLen;
dy *= invEdgeLen;
float2 xAxis, yAxis;
if (cornerID % 2 == 0) {
xAxis = -float2(dx.yzwx[cornerID], dy.yzwx[cornerID]);
yAxis = float2(dx.xyzw[cornerID], dy.xyzw[cornerID]);
} else {
xAxis = float2(dx.xyzw[cornerID], dy.xyzw[cornerID]);
yAxis = -float2(dx.yzwx[cornerID], dy.yzwx[cornerID]);
}
// Calculate local coordinate for the vertex
float2 localPos = position + (joinScale * mirrorOffset * position.yx);
bool snapToCenter = false;
if (normalScale < 0.0) {
// Vertex is inset from the base shape, so we scale by (cornerRadii - strokeRadius)
// and have to check for the possibility of an inner miter. It is always inset by an
// additional conservative AA amount.
if (centerWeight * center.z != 0.0 || (center.w < 0.0 && normalScale < 0.0)) {
snapToCenter = true;
} else {
float localAARadius = center.w; // Only used when center.w >= 0
float2 insetRadii =
cornerRadii + (bidirectionalCoverage ? -strokeRadius : strokeRadius);
if (joinScale == kMiterScale ||
insetRadii.x <= localAARadius || insetRadii.y <= localAARadius) {
// Miter the inset position
localPos = (insetRadii - localAARadius);
} else {
localPos = insetRadii*localPos - localAARadius*normal;
}
}
} else {
// Vertex is outset from the base shape (and possibly with an additional AA outset later
// in device space).
localPos = (cornerRadii + strokeRadius) * localPos;
}
if (snapToCenter) {
localPos = center.xy;
} else {
localPos -= cornerRadii;
localPos = float2(xs[cornerID], ys[cornerID]) + xAxis*localPos.x + yAxis*localPos.y;
}
// Calculate edge distances and device space coordinate for the vertex
// TODO: Apply edge AA flags to these values to turn off AA when necessary.
edgeDistances = dy*(xs - localPos.x) - dx*(ys - localPos.y);
float3x3 localToDevice = float3x3(mat0, mat1, mat2);
// NOTE: This 3x3 inverse is different than just taking the 1st two columns of the 4x4
// inverse of the original SkM44 local-to-device matrix. We could calculate the 3x3 inverse
// and upload it, but it does not seem to be a bottleneck and saves on bandwidth to
// calculate it here instead.
float3x3 deviceToLocal = inverse(localToDevice);
float3 devPos = localToDevice * localPos.xy1;
jacobian = float4(deviceToLocal[0].xy - deviceToLocal[0].z*localPos,
deviceToLocal[1].xy - deviceToLocal[1].z*localPos);
if (deviceSpaceDistances) {
// Apply the Jacobian in the vertex shader so any quadrilateral normals do not have to
// be passed to the fragment shader. However, it's important to use the Jacobian at a
// vertex on the edge, not the current vertex's Jacobian.
float4 gx = -dy*(deviceToLocal[0].x - deviceToLocal[0].z*xs) +
dx*(deviceToLocal[0].y - deviceToLocal[0].z*ys);
float4 gy = -dy*(deviceToLocal[1].x - deviceToLocal[1].z*xs) +
dx*(deviceToLocal[1].y - deviceToLocal[1].z*ys);
// NOTE: The gradient is missing a W term so edgeDistances must still be multiplied by
// 1/w in the fragment shader. The same goes for the encoded coverage scale.
edgeDistances *= inversesqrt(gx*gx + gy*gy);
float2 dim = edgeDistances.xy + edgeDistances.zw;
// TODO: Mixed AA flags should always use the (1,0.5) scale and bias since the set of
// tiled quads forms a larger shape that would not get subpixel treatment.
perPixelControl.y = 1.0 + min(min(dim.x, dim.y), abs(devPos.z));
}
// Only outset for a vertex that is in front of the w=0 plane to avoid dealing with outset
// triangles rasterizing differently from the main triangles as w crosses 0.
if (normalScale > 0.0 && devPos.z > 0.0) {
// Note that when there's no perspective, the jacobian is equivalent to the normal
// matrix (inverse transpose), but produces correct results when there's perspective
// because it accounts for the position's influence on a line's projected direction.
float s = sign(xAxis.x*yAxis.y - yAxis.x*xAxis.y);
float2x2 J = float2x2(jacobian.xy, jacobian.zw);
float2 nx = s * cornerAspectRatio.x * normal.x * perp(-yAxis) * J;
float2 ny = s * cornerAspectRatio.y * normal.y * perp( xAxis) * J;
bool isMidVertex = normal.x != 0.0 && normal.y != 0.0;
if (joinScale == kMiterScale && isMidVertex) {
// Produce a bisecting vector in device space (ignoring 'normal' since that was
// previously corrected to match the mitered edge normals).
nx = normalize(nx);
ny = normalize(ny);
if (dot(nx, ny) < -0.8) {
// Normals are in nearly opposite directions, so adjust to avoid float error.
float s = sign(cross_length_2d(nx, ny));
nx = s*perp(nx);
ny = -s*perp(ny);
}
}
// Adding the normal components together directly results in what we'd have
// calculated if we'd just transformed 'normal' in one go, assuming they weren't
// normalized in the if-block above. If they were normalized, the sum equals the
// bisector between the original nx and ny.
//
// We multiply by W so that after perspective division the new point is offset by the
// now-unit normal.
devPos.xy += devPos.z * normalize(nx + ny);
// By construction these points are 1px away from the outer edge in device space.
if (deviceSpaceDistances) {
// Apply directly to edgeDistances to save work per pixel later on.
edgeDistances -= devPos.z;
} else {
// Otherwise store separately so edgeDistances can be used to reconstruct corner pos
perPixelControl.y = -devPos.z;
}
} else if (!deviceSpaceDistances) {
// Triangles are within the original shape so there's no additional outsetting to
// take into account for coverage calculations.
perPixelControl.y = 0.0;
}
if (centerWeight != 0.0) {
// A positive value signals that a pixel is trivially full coverage.
perPixelControl.x = 1.0;
} else {
// A negative value signals bidirectional coverage, and a zero value signals a solid
// interior with per-pixel coverage.
perPixelControl.x = bidirectionalCoverage ? -1.0 : 0.0;
}
// Write out final results
stepLocalCoords = localPos;
float4 devPosition = float4(devPos.xy, devPos.z*depth, devPos.z);
)";
}
const char* AnalyticRRectRenderStep::fragmentCoverageSkSL() const {
// TODO: Further modularize this
return R"(
if (perPixelControl.x > 0.0) {
// A trivially solid interior pixel, either from a filled rect or round rect, or a
// stroke with sufficiently large width that the interior completely overlaps itself.
outputCoverage = half4(1.0);
} else if (perPixelControl.y > 1.0) {
// This represents a filled rectangle or quadrilateral, where the distances have already
// been converted to device space. Mitered strokes cannot use this optimization because
// their scale and bias is not uniform over the shape; Rounded shapes cannot use this
// because they rely on the edge distances being in local space to reconstruct the
// per-corner positions for the elliptical implicit functions.
float2 outerDist = min(edgeDistances.xy, edgeDistances.zw);
float c = min(outerDist.x, outerDist.y) * sk_FragCoord.w;
float scale = (perPixelControl.y - 1.0) * sk_FragCoord.w;
float bias = coverage_bias(scale);
outputCoverage = half4(clamp(scale * (c + bias), 0.0, 1.0));
} else {
// Compute per-pixel coverage, mixing four outer edge distances, possibly four inner
// edge distances, and per-corner elliptical distances into a final coverage value.
// The Jacobian needs to be multiplied by W, but sk_FragCoord.w stores 1/w.
float2x2 J = float2x2(jacobian.xy, jacobian.zw) / sk_FragCoord.w;
float2 invGradLen = float2(inverse_grad_len(float2(1.0, 0.0), J),
inverse_grad_len(float2(0.0, 1.0), J));
float2 outerDist = invGradLen * (strokeParams.x + min(edgeDistances.xy,
edgeDistances.zw));
// d.x tracks minimum outer distance (pre scale-and-biasing to a coverage value).
// d.y tracks negative maximum inner distance (so min() over c accumulates min and outer
// and max inner simultaneously).)
float2 d = float2(min(outerDist.x, outerDist.y), -1.0);
float scale, bias;
// Check for bidirectional coverage, which is is marked as a -1 from the vertex shader.
// We don't just check for < 0 since extrapolated fill triangle samples can have small
// negative values.
if (perPixelControl.x > -0.95) {
// A solid interior, so update scale and bias based on full width and height
float2 dim = invGradLen * (edgeDistances.xy + edgeDistances.zw + 2*strokeParams.xx);
scale = min(min(dim.x, dim.y), 1.0);
bias = coverage_bias(scale);
// Since we leave d.y = -1.0, no inner curve coverage will adjust it closer to 0,
// so 'finalCoverage' is based solely on outer edges and curves.
} else {
// Bidirectional coverage, so we modify c.y to hold the negative of the maximum
// interior coverage, and update scale and bias based on stroke width.
float2 strokeWidth = 2.0 * strokeParams.x * invGradLen;
float2 innerDist = strokeWidth - outerDist;
d.y = -max(innerDist.x, innerDist.y);
if (strokeParams.x > 0.0) {
float strokeDim = min(strokeWidth.x, strokeWidth.y);
if (innerDist.y >= -0.5 && strokeWidth.y > strokeDim) {
strokeDim = strokeWidth.y;
}
if (innerDist.x >= -0.5 && strokeWidth.x > strokeDim) {
strokeDim = strokeWidth.x;
}
scale = min(strokeDim, 1.0);
bias = coverage_bias(scale);
} else {
// A hairline, so scale and bias should both be 1
scale = bias = 1.0;
}
}
// Check all corners, although most pixels should only be influenced by 1.
corner_distances(d, J, strokeParams, edgeDistances, xRadii, yRadii);
float outsetDist = min(perPixelControl.y, 0.0) * sk_FragCoord.w;
float finalCoverage = scale * (min(d.x + outsetDist, -d.y) + bias);
outputCoverage = half4(clamp(finalCoverage, 0.0, 1.0));
}
)";
}
void AnalyticRRectRenderStep::writeVertices(DrawWriter* writer,
const DrawParams& params,
int ssboIndex) const {
SkASSERT(params.geometry().isShape() || params.geometry().isEdgeAAQuad());
DrawWriter::Instances instance{*writer, fVertexBuffer, fIndexBuffer, kIndexCount};
auto vw = instance.append(1);
// The bounds of a rect is the rect, and the bounds of a rrect is tight (== SkRRect::getRect()).
Rect bounds = params.geometry().bounds();
// aaRadius will be set to a negative value to signal a complex self-intersection that has to
// be calculated in the vertex shader.
float aaRadius = local_aa_radius(params.transform(), bounds);
float strokeInset = 0.f;
float centerWeight = kSolidInterior;
if (params.isStroke()) {
const Shape& shape = params.geometry().shape(); // EdgeAAQuads are not stroked
SkASSERT(params.strokeStyle().halfWidth() >= 0.f);
SkASSERT(shape.isRect() || params.strokeStyle().halfWidth() == 0.f ||
(shape.isRRect() && SkRRectPriv::AllCornersCircular(shape.rrect())));
const float strokeRadius = params.strokeStyle().halfWidth();
skvx::float2 innerGap = bounds.size() - 2.f * params.strokeStyle().halfWidth();
if (any(innerGap <= 0.f)) {
// AA inset intersections are measured from the *outset*
strokeInset = -strokeRadius;
} else {
// This will be upgraded to kFilledStrokeInterior if insets intersect
centerWeight = kStrokeInterior;
strokeInset = strokeRadius;
}
skvx::float4 xRadii = shape.isRRect() ? load_x_radii(shape.rrect()) : skvx::float4(0.f);
if (params.strokeStyle().halfWidth() > 0.f) {
float joinStyle = params.strokeStyle().joinLimit();
if (params.strokeStyle().isMiterJoin()) {
// All corners are 90-degrees so become beveled if the miter limit is < sqrt(2).
if (params.strokeStyle().miterLimit() < SK_ScalarSqrt2) {
joinStyle = 0.f; // == bevel
} else {
// Discard actual miter limit because a 90-degree corner never exceeds it.
joinStyle = 1.f;
}
}
// Write a negative value outside [-1, 0] to signal a stroked shape, then the style
// params, followed by corner radii and bounds.
vw << -2.f << 0.f << strokeRadius << joinStyle << xRadii << bounds.ltrb();
} else {
// Write -2 - cornerRadii to encode the X radii in such a way to trigger stroking but
// guarantee the 2nd field is non-zero to signal hairline. Then we upload Y radii as
// well to allow for elliptical hairlines.
skvx::float4 yRadii = shape.isRRect() ? load_y_radii(shape.rrect()) : skvx::float4(0.f);
vw << (-2.f - xRadii) << yRadii << bounds.ltrb();
}
} else {
if (params.geometry().isEdgeAAQuad()) {
// NOTE: If quad.isRect() && quad.edgeFlags() == kAll, the written data is identical to
// Shape.isRect() case below.
const EdgeAAQuad& quad = params.geometry().edgeAAQuad();
// -1 for AA on, 0 for AA off
auto edgeSigns = skvx::float4{quad.edgeFlags() & AAFlags::kLeft ? -1.f : 0.f,
quad.edgeFlags() & AAFlags::kTop ? -1.f : 0.f,
quad.edgeFlags() & AAFlags::kRight ? -1.f : 0.f,
quad.edgeFlags() & AAFlags::kBottom ? -1.f : 0.f};
vw << edgeSigns << quad.xs() << quad.ys();
} else {
const Shape& shape = params.geometry().shape();
if (shape.isRect() || (shape.isRRect() && shape.rrect().isRect())) {
// Rectangles (or rectangles embedded in an SkRRect) are converted to the
// quadrilateral case, but with all edges anti-aliased (== -1).
skvx::float4 ltrb = bounds.ltrb();
vw << /*edge flags*/ skvx::float4(-1.f)
<< /*xs*/ skvx::shuffle<0,2,2,0>(ltrb)
<< /*ys*/ skvx::shuffle<1,1,3,3>(ltrb);
} else {
// A filled rounded rectangle, so make sure at least one corner radii > 0 or the
// shader won't detect it as a rounded rect.
SkASSERT(any(load_x_radii(shape.rrect()) > 0.f));
vw << load_x_radii(shape.rrect()) << load_y_radii(shape.rrect()) << bounds.ltrb();
}
}
}
if (opposite_insets_intersect(params.geometry(), strokeInset, aaRadius)) {
aaRadius = kComplexAAInsets;
if (centerWeight == kStrokeInterior) {
centerWeight = kFilledStrokeInterior;
}
}
// All instance types share the remaining instance attribute definitions
const SkM44& m = params.transform().matrix();
vw << bounds.center() << centerWeight << aaRadius
<< params.order().depthAsFloat()
<< ssboIndex
<< m.rc(0,0) << m.rc(1,0) << m.rc(3,0) // mat0
<< m.rc(0,1) << m.rc(1,1) << m.rc(3,1) // mat1
<< m.rc(0,3) << m.rc(1,3) << m.rc(3,3); // mat2
}
void AnalyticRRectRenderStep::writeUniformsAndTextures(const DrawParams&,
PipelineDataGatherer*) const {
// All data is uploaded as instance attributes, so no uniforms are needed.
}
} // namespace skgpu::graphite