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/*
* Copyright 2021 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef skgpu_tessellate_CullTest_DEFINED
#define skgpu_tessellate_CullTest_DEFINED
#include "include/core/SkMatrix.h"
#include "include/core/SkPoint.h"
#include "include/core/SkRect.h"
#include "include/private/base/SkAssert.h"
#include "src/base/SkVx.h"
namespace skgpu::tess {
// This class determines whether the given local-space points will be contained in the cull bounds
// post transform. For the versions that take >1 point, it returns whether any region of their
// device-space bounding box will be in the cull bounds.
//
// NOTE: Our view matrix is not a normal matrix. M*p maps to the float4 [x, y, -x, -y] in device
// space. We do this to aid in quick bounds calculations. The matrix also does not have a
// translation element. Instead we unapply the translation to the cull bounds ahead of time.
class CullTest {
public:
CullTest() = default;
CullTest(const SkRect& devCullBounds, const SkMatrix& m) {
this->set(devCullBounds, m);
}
void set(const SkRect& devCullBounds, const SkMatrix& m) {
SkASSERT(!m.hasPerspective());
// [fMatX, fMatY] maps path coordinates to the float4 [x, y, -x, -y] in device space.
fMatX = {m.getScaleX(), m.getSkewY(), -m.getScaleX(), -m.getSkewY()};
fMatY = {m.getSkewX(), m.getScaleY(), -m.getSkewX(), -m.getScaleY()};
// Store the cull bounds as [l, t, -r, -b] for faster math.
// Also subtract the matrix translate from the cull bounds ahead of time, rather than adding
// it to every point every time we test.
fCullBounds = {devCullBounds.fLeft - m.getTranslateX(),
devCullBounds.fTop - m.getTranslateY(),
m.getTranslateX() - devCullBounds.fRight,
m.getTranslateY() - devCullBounds.fBottom};
}
// Returns whether M*p will be in the viewport.
bool isVisible(SkPoint p) const {
// devPt = [x, y, -x, -y] in device space.
auto devPt = fMatX*p.fX + fMatY*p.fY;
// i.e., l < x && t < y && r > x && b > y.
return all(fCullBounds < devPt);
}
// Returns whether any region of the bounding box of M * p0..2 will be in the viewport.
bool areVisible3(const SkPoint p[3]) const {
// Transform p0..2 to device space.
auto val0 = fMatY * p[0].fY;
auto val1 = fMatY * p[1].fY;
auto val2 = fMatY * p[2].fY;
val0 = fMatX*p[0].fX + val0;
val1 = fMatX*p[1].fX + val1;
val2 = fMatX*p[2].fX + val2;
// At this point: valN = {xN, yN, -xN, -yN} in device space.
// Find the device-space bounding box of p0..2.
val0 = max(val0, val1);
val0 = max(val0, val2);
// At this point: val0 = [r, b, -l, -t] of the device-space bounding box of p0..2.
// Does fCullBounds intersect the device-space bounding box of p0..2?
// i.e., l0 < r1 && t0 < b1 && r0 > l1 && b0 > t1.
return all(fCullBounds < val0);
}
// Returns whether any region of the bounding box of M * p0..3 will be in the viewport.
bool areVisible4(const SkPoint p[4]) const {
// Transform p0..3 to device space.
auto val0 = fMatY * p[0].fY;
auto val1 = fMatY * p[1].fY;
auto val2 = fMatY * p[2].fY;
auto val3 = fMatY * p[3].fY;
val0 = fMatX*p[0].fX + val0;
val1 = fMatX*p[1].fX + val1;
val2 = fMatX*p[2].fX + val2;
val3 = fMatX*p[3].fX + val3;
// At this point: valN = {xN, yN, -xN, -yN} in device space.
// Find the device-space bounding box of p0..3.
val0 = max(val0, val1);
val2 = max(val2, val3);
val0 = max(val0, val2);
// At this point: val0 = [r, b, -l, -t] of the device-space bounding box of p0..3.
// Does fCullBounds intersect the device-space bounding box of p0..3?
// i.e., l0 < r1 && t0 < b1 && r0 > l1 && b0 > t1.
return all(fCullBounds < val0);
}
private:
// [fMatX, fMatY] maps path coordinates to the float4 [x, y, -x, -y] in device space.
skvx::float4 fMatX;
skvx::float4 fMatY;
skvx::float4 fCullBounds; // [l, t, -r, -b]
};
} // namespace skgpu::tess
#endif // skgpu_tessellate_CullTest_DEFINED