src/gpu/graphite/render/TessellateStrokesRenderStep.cpp

/*
 * 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/TessellateStrokesRenderStep.h"

#include "include/core/SkM44.h"
#include "include/core/SkMatrix.h"
#include "include/core/SkPath.h"
#include "include/core/SkPoint.h"
#include "include/core/SkSpan.h"
#include "include/core/SkStrokeRec.h"
#include "include/private/SkAssert.h"
#include "include/private/SkAttributes.h"
#include "include/private/SkDebug.h"
#include "include/private/SkEnumBitMask.h"
#include "src/core/SkGeometry.h"
#include "src/core/SkSLTypeShared.h"
#include "src/core/SkVx.h"
#include "src/gpu/graphite/Attribute.h"
#include "src/gpu/graphite/DrawOrder.h"
#include "src/gpu/graphite/DrawParams.h"
#include "src/gpu/graphite/DrawTypes.h"
#include "src/gpu/graphite/PipelineData.h"
#include "src/gpu/graphite/ResourceTypes.h"
#include "src/gpu/graphite/geom/Geometry.h"
#include "src/gpu/graphite/geom/Shape.h"
#include "src/gpu/graphite/geom/Transform.h"
#include "src/gpu/graphite/render/CommonDepthStencilSettings.h"
#include "src/gpu/graphite/render/DynamicInstancesPatchAllocator.h"
#include "src/gpu/tessellate/FixedCountBufferUtils.h"
#include "src/gpu/tessellate/PatchWriter.h"
#include "src/gpu/tessellate/StrokeIterator.h"
#include "src/gpu/tessellate/Tessellation.h"
#include "src/gpu/tessellate/WangsFormula.h"
#include "src/sksl/SkSLString.h"

namespace skgpu::graphite {

namespace {

using namespace skgpu::tess;

// Always use dynamic stroke params and join control points, track the join control point in
// PatchWriter and replicate line end points (match Ganesh's shader behavior).
//
// No explicit curve type on platforms that support infinity.
// No color or wide color attribs, since it might always be part of the PaintParams
// or we'll add a color-only fast path to RenderStep later.
static constexpr PatchAttribs kAttribs = PatchAttribs::kJoinControlPoint |
                                         PatchAttribs::kStrokeParams |
                                         PatchAttribs::kPaintDepth |
                                         PatchAttribs::kSsboIndex;
static constexpr PatchAttribs kAttribsWithCurveType = kAttribs | PatchAttribs::kExplicitCurveType;
using Writer = PatchWriter<DynamicInstancesPatchAllocator<FixedCountStrokes>,
                           Required<PatchAttribs::kJoinControlPoint>,
                           Required<PatchAttribs::kStrokeParams>,
                           Required<PatchAttribs::kPaintDepth>,
                           Required<PatchAttribs::kSsboIndex>,
                           Optional<PatchAttribs::kExplicitCurveType>,
                           ReplicateLineEndPoints,
                           TrackJoinControlPoints>;

// The order of the attribute declarations must match the order used by
// PatchWriter::emitPatchAttribs, i.e.:
//     join << fanPoint << stroke << color << depth << curveType << ssboIndex
static constexpr Attribute kBaseAttributes[] = {
        {"p01", VertexAttribType::kFloat4, SkSLType::kFloat4},
        {"p23", VertexAttribType::kFloat4, SkSLType::kFloat4},
        {"prevPoint", VertexAttribType::kFloat2, SkSLType::kFloat2},
        {"stroke", VertexAttribType::kFloat2, SkSLType::kFloat2},
        {"depth", VertexAttribType::kFloat, SkSLType::kFloat},
        {"ssboIndex", VertexAttribType::kUInt, SkSLType::kUInt}};

static constexpr Attribute kAttributesWithCurveType[] = {
        {"p01", VertexAttribType::kFloat4, SkSLType::kFloat4},
        {"p23", VertexAttribType::kFloat4, SkSLType::kFloat4},
        {"prevPoint", VertexAttribType::kFloat2, SkSLType::kFloat2},
        {"stroke", VertexAttribType::kFloat2, SkSLType::kFloat2},
        {"depth", VertexAttribType::kFloat, SkSLType::kFloat},
        {"curveType", VertexAttribType::kFloat, SkSLType::kFloat},
        {"ssboIndex", VertexAttribType::kUInt, SkSLType::kUInt}};

static constexpr SkSpan<const Attribute> kAttributes[2] = {kAttributesWithCurveType,
                                                           kBaseAttributes};

}  // namespace

TessellateStrokesRenderStep::TessellateStrokesRenderStep(Layout layout,
                                                         RenderStepID renderStepId,
                                                         SkEnumBitMask<Flags> xtraFlags,
                                                         bool infinitySupport,
                                                         StencilSettings stencilSettings)
        : RenderStep(layout,
                     renderStepId,
                     Flags::kRequiresMSAA | Flags::kAppendDynamicInstances | xtraFlags,
                     /*uniforms=*/{{"affineMatrix", SkSLType::kFloat4},
                                   {"translate", SkSLType::kFloat2},
                                   {"maxScale", SkSLType::kFloat}},
                     PrimitiveType::kTriangleStrip,
                     stencilSettings,
                     /*staticAttrs=*/ {},
                     /*appendAttrs=*/SK_UNSAFE_TODO(kAttributes[infinitySupport]),
                     /*storageUniforms=*/{})
        , fInfinitySupport(infinitySupport) {}

TessellateStrokesRenderStep::~TessellateStrokesRenderStep() {}

std::unique_ptr<TessellateStrokesRenderStep> TessellateStrokesRenderStep::Regular(
        Layout layout, bool infinitySupport) {
    // NOTE: The stroke geometry can self intersect and this step performs shading, so do not
    // include `kAllowsSelfIntersection` or `kNoSelfIntersection`. This allows the depth test to
    // eliminate double blending when a transparent stroke crosses over itself.
    return std::unique_ptr<TessellateStrokesRenderStep>(new TessellateStrokesRenderStep(
            layout, RenderStepID::kTessellateStrokes_Fill, Flags::kPerformsShading,
            infinitySupport, /*stencilSettings=*/{}));
}

std::unique_ptr<TessellateStrokesRenderStep> TessellateStrokesRenderStep::StencilOnly(
        Layout layout, bool infinitySupport) {
    // Unlike `Regular()`, this variant can allow self intersections because overlap is gracefully
    // handled by the stencil buffer updates and then any follow-up cover step will shade once.
    return std::unique_ptr<TessellateStrokesRenderStep>(new TessellateStrokesRenderStep(
            layout, RenderStepID::kTessellateStrokes_Stencil, Flags::kAllowsSelfIntersection,
            infinitySupport, kIncrementStencilPass));
}

std::string TessellateStrokesRenderStep::vertexSkSL(const RootNodesInfo&) const {
    // TODO: Assumes vertex ID support for now, max edges must equal
    // skgpu::tess::FixedCountStrokes::kMaxEdges -> (2^14 - 1) -> 16383
    return SK_UNSAFE_TODO(SkSL::String::printf(
            "float edgeID = float(sk_VertexID >> 1);\n"
            "if ((sk_VertexID & 1) != 0) {"
                "edgeID = -edgeID;"
            "}\n"
            "float2x2 affine = float2x2(affineMatrix.xy, affineMatrix.zw);\n"
            "float4 devAndLocalCoords = tessellate_stroked_curve("
                    "edgeID, 16383, affine, translate, maxScale, p01, p23, prevPoint,"
                    "stroke, %s);\n"
            "float4 devPosition = float4(devAndLocalCoords.xy, depth, 1.0);\n"
            "stepLocalCoords = devAndLocalCoords.zw;\n",
            fInfinitySupport ? "curve_type_using_inf_support(p23)" : "curveType"));
}

void TessellateStrokesRenderStep::writeVertices(DrawWriter* dw,
                                                StorageContext* /*storageContext*/,
                                                const DrawParams& params,
                                                uint32_t ssboIndex) const {
    SkPath path = params.geometry().shape().asPath(); // TODO: Iterate the Shape directly

    int patchReserveCount = FixedCountStrokes::PreallocCount(path.countVerbs());
    // Stroke tessellation does not use fixed indices or vertex data, and only needs the vertex ID
    static const BindBufferInfo kNullBinding = {};
    // TODO: All HW that Graphite will run on should support instancing ith sk_VertexID, but when
    // we support Vulkan+Swiftshader, we will need the vertex buffer ID fallback unless Swiftshader
    // has figured out how to support vertex IDs before then.
    Writer writer{fInfinitySupport ? kAttribs : kAttribsWithCurveType,
                  *dw,
                  kNullBinding,
                  kNullBinding,
                  patchReserveCount};
    writer.updatePaintDepthAttrib(params.order().depthAsFloat());
    writer.updateSsboIndexAttrib(ssboIndex);

    // The vector xform approximates how the control points are transformed by the shader to
    // more accurately compute how many *parametric* segments are needed.
    // getMaxScale() returns -1 if it can't compute a scale factor (e.g. perspective), taking the
    // absolute value automatically converts that to an identity scale factor for our purposes.
    writer.setShaderTransform(wangs_formula::VectorXform{params.transform().matrix()},
                              params.transform().maxScaleFactor());

    SkASSERT(params.isStroke());
    writer.updateStrokeParamsAttrib({params.strokeStyle().halfWidth(),
                                     params.strokeStyle().joinLimit()});

    for (auto [verb, pts, w] : SkPathPriv::Iterate(path)) {
        switch (verb) {
            case SkPathVerb::kMove:
                // This automatically joins the last contour with the first contour (deferred) if
                // the contour is closed. If the contour is not closed, it automatically adds
                // additional patches for the end cap of the last patch and the beginning cap of the
                // deferred patch. This does nothing if this is the beginning of the first contour.
                writer.writeDeferredStrokePatch(pts[0], params.strokeStyle().cap());
                break;

            case SkPathVerb::kClose:
                // Draws a line back to the starting point of the contour and writes any deferred
                // patch with a join (instead of caps). Or if the contour was empty, draws a cap.
                // Since any deferred patch is consumed, the next moveTo's writeDeferredStrokePatch
                // will do nothing but record the beginning of the new contour.
                writer.closeDeferredStrokePatch(params.strokeStyle().cap());
                break;

            case SkPathVerb::kLine:
                writer.writeLine(pts[0], SK_UNSAFE_TODO(pts[1]));
                break;

            case SkPathVerb::kQuad:
                if (ConicHasCusp(pts)) {
                    // The cusp is always at the midtangent.
                    SkPoint cusp = SkEvalQuadAt(pts, SkFindQuadMidTangent(pts));
                    writer.writeCircle(cusp);
                    // A quad can only have a cusp if it's flat with a 180-degree turnaround.
                    writer.writeLine(pts[0], cusp);
                    writer.writeLine(cusp, SK_UNSAFE_TODO(pts[2]));
                } else {
                    writer.writeQuadratic(pts);
                }
                break;

            case SkPathVerb::kConic:
                if (ConicHasCusp(pts)) {
                    // The cusp is always at the midtangent.
                    SkConic conic(pts, *w);
                    SkPoint cusp = conic.evalAt(conic.findMidTangent());
                    writer.writeCircle(cusp);
                    // A conic can only have a cusp if it's flat with a 180-degree turnaround.
                    writer.writeLine(pts[0], cusp);
                    writer.writeLine(cusp, SK_UNSAFE_TODO(pts[2]));
                } else {
                    writer.writeConic(pts, *w);
                }
                break;

            case SkPathVerb::kCubic: {
                SkPoint chops[10];
                float T[2];
                bool areCusps;
                int numChops = FindCubicConvex180Chops(pts, T, &areCusps);
                if (numChops == 0) {
                    writer.writeCubic(pts);
                } else if (numChops == 1) {
                    SkChopCubicAt(pts, chops, T[0]);
                    if (areCusps) {
                        writer.writeCircle(chops[3]);
                        // In a perfect world, these 3 points would be be equal after chopping
                        // on a cusp.
                        chops[2] = chops[4] = chops[3];
                    }
                    writer.writeCubic(chops);
                    writer.writeCubic(SK_UNSAFE_TODO(chops + 3));
                } else {
                    SkASSERT(numChops == 2);
                    SkChopCubicAt(pts, chops, T[0], T[1]);
                    if (areCusps) {
                        writer.writeCircle(chops[3]);
                        writer.writeCircle(chops[6]);
                        // Two cusps are only possible if it's a flat line with two 180-degree
                        // turnarounds.
                        writer.writeLine(chops[0], chops[3]);
                        writer.writeLine(chops[3], chops[6]);
                        writer.writeLine(chops[6], chops[9]);
                    } else {
                        writer.writeCubic(chops);
                        writer.writeCubic(SK_UNSAFE_TODO(chops + 3));
                        writer.writeCubic(SK_UNSAFE_TODO(chops + 6));
                    }
                }
                break;
            }
        }
    }

    // Finish the last contour (next moveTo point doesn't matter)
    writer.writeDeferredStrokePatch({0.f, 0.f}, params.strokeStyle().cap());
}

void TessellateStrokesRenderStep::writeUniformsAndTextures(const DrawParams& params,
                                                           PipelineDataGatherer* gatherer) const {
    SkDEBUGCODE(gatherer->checkRewind());
    // TODO: Implement perspective
    SkASSERT(params.transform().type() < Transform::Type::kPerspective);

    SkDEBUGCODE(UniformExpectationsValidator uev(gatherer, this->uniforms());)

    // affineMatrix = float4 (2x2 of transform), translate = float2, maxScale = float
    // Column-major 2x2 of the transform.
    SkV4 upper = {params.transform().matrix().rc(0, 0), params.transform().matrix().rc(1, 0),
                  params.transform().matrix().rc(0, 1), params.transform().matrix().rc(1, 1)};
    gatherer->write(upper);

    gatherer->write(SkPoint{params.transform().matrix().rc(0, 3),
                            params.transform().matrix().rc(1, 3)});

    gatherer->write(params.transform().maxScaleFactor());
}

}  // namespace skgpu::graphite