src/core/SkDraw_vertices.cpp

/*
 * Copyright 2017 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/core/SkString.h"
#include "include/private/SkNx.h"
#include "src/core/SkArenaAlloc.h"
#include "src/core/SkAutoBlitterChoose.h"
#include "src/core/SkConvertPixels.h"
#include "src/core/SkCoreBlitters.h"
#include "src/core/SkDraw.h"
#include "src/core/SkMatrixProvider.h"
#include "src/core/SkRasterClip.h"
#include "src/core/SkRasterPipeline.h"
#include "src/core/SkScan.h"
#include "src/core/SkVM.h"
#include "src/core/SkVertState.h"
#include "src/core/SkVerticesPriv.h"
#include "src/shaders/SkComposeShader.h"
#include "src/shaders/SkShaderBase.h"

struct Matrix43 {
    float fMat[12];    // column major

    Sk4f map(float x, float y) const {
        return Sk4f::Load(&fMat[0]) * x + Sk4f::Load(&fMat[4]) * y + Sk4f::Load(&fMat[8]);
    }

    // Pass a by value, so we don't have to worry about aliasing with this
    void setConcat(const Matrix43 a, const SkMatrix& b) {
        SkASSERT(!b.hasPerspective());

        fMat[ 0] = a.dot(0, b.getScaleX(), b.getSkewY());
        fMat[ 1] = a.dot(1, b.getScaleX(), b.getSkewY());
        fMat[ 2] = a.dot(2, b.getScaleX(), b.getSkewY());
        fMat[ 3] = a.dot(3, b.getScaleX(), b.getSkewY());

        fMat[ 4] = a.dot(0, b.getSkewX(), b.getScaleY());
        fMat[ 5] = a.dot(1, b.getSkewX(), b.getScaleY());
        fMat[ 6] = a.dot(2, b.getSkewX(), b.getScaleY());
        fMat[ 7] = a.dot(3, b.getSkewX(), b.getScaleY());

        fMat[ 8] = a.dot(0, b.getTranslateX(), b.getTranslateY()) + a.fMat[ 8];
        fMat[ 9] = a.dot(1, b.getTranslateX(), b.getTranslateY()) + a.fMat[ 9];
        fMat[10] = a.dot(2, b.getTranslateX(), b.getTranslateY()) + a.fMat[10];
        fMat[11] = a.dot(3, b.getTranslateX(), b.getTranslateY()) + a.fMat[11];
    }

private:
    float dot(int index, float x, float y) const {
        return fMat[index + 0] * x + fMat[index + 4] * y;
    }
};

static bool SK_WARN_UNUSED_RESULT
texture_to_matrix(const VertState& state, const SkPoint verts[], const SkPoint texs[],
                  SkMatrix* matrix) {
    SkPoint src[3], dst[3];

    src[0] = texs[state.f0];
    src[1] = texs[state.f1];
    src[2] = texs[state.f2];
    dst[0] = verts[state.f0];
    dst[1] = verts[state.f1];
    dst[2] = verts[state.f2];
    return matrix->setPolyToPoly(src, dst, 3);
}

class SkTriColorShader : public SkShaderBase {
public:
    SkTriColorShader(bool isOpaque, bool usePersp) : fIsOpaque(isOpaque), fUsePersp(usePersp) {}

    // This gets called for each triangle, without re-calling onAppendStages.
    bool update(const SkMatrix& ctmInv, const SkPoint pts[], const SkPMColor4f colors[],
                int index0, int index1, int index2);

protected:
#ifdef SK_ENABLE_LEGACY_SHADERCONTEXT
    Context* onMakeContext(const ContextRec& rec, SkArenaAlloc* alloc) const override {
        return nullptr;
    }
#endif
    bool onAppendStages(const SkStageRec& rec) const override {
        rec.fPipeline->append(SkRasterPipeline::seed_shader);
        if (fUsePersp) {
            rec.fPipeline->append(SkRasterPipeline::matrix_perspective, &fM33);
        }
        rec.fPipeline->append(SkRasterPipeline::matrix_4x3, &fM43);
        return true;
    }

    skvm::Color onProgram(skvm::Builder*,
                          skvm::Coord, skvm::Coord, skvm::Color,
                          const SkMatrixProvider&, const SkMatrix*, const SkColorInfo&,
                          skvm::Uniforms*, SkArenaAlloc*) const override {
        // TODO?
        return {};
    }

private:
    bool isOpaque() const override { return fIsOpaque; }
    // For serialization.  This will never be called.
    Factory getFactory() const override { return nullptr; }
    const char* getTypeName() const override { return nullptr; }

    // If fUsePersp, we need both of these matrices,
    // otherwise we can combine them, and only use fM43

    Matrix43 fM43;
    SkMatrix fM33;
    const bool fIsOpaque;
    const bool fUsePersp;   // controls our stages, and what we do in update()

    using INHERITED = SkShaderBase;
};

bool SkTriColorShader::update(const SkMatrix& ctmInv, const SkPoint pts[],
                              const SkPMColor4f colors[], int index0, int index1, int index2) {
    SkMatrix m, im;
    m.reset();
    m.set(0, pts[index1].fX - pts[index0].fX);
    m.set(1, pts[index2].fX - pts[index0].fX);
    m.set(2, pts[index0].fX);
    m.set(3, pts[index1].fY - pts[index0].fY);
    m.set(4, pts[index2].fY - pts[index0].fY);
    m.set(5, pts[index0].fY);
    if (!m.invert(&im)) {
        return false;
    }

    fM33.setConcat(im, ctmInv);

    Sk4f c0 = Sk4f::Load(colors[index0].vec()),
         c1 = Sk4f::Load(colors[index1].vec()),
         c2 = Sk4f::Load(colors[index2].vec());

    (c1 - c0).store(&fM43.fMat[0]);
    (c2 - c0).store(&fM43.fMat[4]);
    c0.store(&fM43.fMat[8]);

    if (!fUsePersp) {
        fM43.setConcat(fM43, fM33);
    }
    return true;
}

// Convert the SkColors into float colors. The conversion depends on some conditions:
// - If the pixmap has a dst colorspace, we have to be "color-correct".
//   Do we map into dst-colorspace before or after we interpolate?
// - We have to decide when to apply per-color alpha (before or after we interpolate)
//
// For now, we will take a simple approach, but recognize this is just a start:
// - convert colors into dst colorspace before interpolation (matches gradients)
// - apply per-color alpha before interpolation (matches old version of vertices)
//
static SkPMColor4f* convert_colors(const SkColor src[], int count, SkColorSpace* deviceCS,
                                   SkArenaAlloc* alloc) {
    SkPMColor4f* dst = alloc->makeArray<SkPMColor4f>(count);
    SkImageInfo srcInfo = SkImageInfo::Make(count, 1, kBGRA_8888_SkColorType,
                                            kUnpremul_SkAlphaType, SkColorSpace::MakeSRGB());
    SkImageInfo dstInfo = SkImageInfo::Make(count, 1, kRGBA_F32_SkColorType,
                                            kPremul_SkAlphaType, sk_ref_sp(deviceCS));
    SkAssertResult(SkConvertPixels(dstInfo, dst, 0, srcInfo, src, 0));
    return dst;
}

static bool compute_is_opaque(const SkColor colors[], int count) {
    uint32_t c = ~0;
    for (int i = 0; i < count; ++i) {
        c &= colors[i];
    }
    return SkColorGetA(c) == 0xFF;
}

static void fill_triangle_2(const VertState& state, SkBlitter* blitter, const SkRasterClip& rc,
                            const SkPoint dev2[]) {
    SkPoint tmp[] = {
        dev2[state.f0], dev2[state.f1], dev2[state.f2]
    };
    SkScan::FillTriangle(tmp, rc, blitter);
}

static constexpr int kMaxClippedTrianglePointCount = 4;
static void fill_triangle_3(const VertState& state, SkBlitter* blitter, const SkRasterClip& rc,
                            const SkPoint3 dev3[]) {
    // Compute the crossing point (across zero) for the two values, expressed as a
    // normalized 0...1 value. If curr is 0, returns 0. If next is 0, returns 1.
    auto computeT = [](float curr, float next) {
        // Check that 0 is between next and curr.
        SkASSERT((next <= 0 && 0 < curr) || (curr <= 0 && 0 < next));
        float t = curr / (curr - next);
        SkASSERT(0 <= t && t <= 1);
        return t;
    };

    auto lerp = [](SkPoint3 curr, SkPoint3 next, float t) {
        return curr + t * (next - curr);
    };

    constexpr float tol = 0.05f;
    // tol is the nudge away from zero, to keep the numerics nice.
    // Think of it as our near-clipping-plane (or w-plane).
    auto clip = [&](SkPoint3 curr, SkPoint3 next) {
        // Return the point between curr and next where the fZ value crosses tol.
        // To be (really) perspective correct, we should be computing based on 1/Z, not Z.
        // For now, this is close enough (and faster).
        return lerp(curr, next, computeT(curr.fZ - tol, next.fZ - tol));
    };

    // Clip a triangle (based on its homogeneous W values), and return the projected polygon.
    // Since we only clip against one "edge"/plane, the max number of points in the clipped
    // polygon is 4.
    auto clipTriangle = [&](SkPoint dst[], const int idx[3], const SkPoint3 pts[]) -> int {
        SkPoint3 outPoints[kMaxClippedTrianglePointCount];
        SkPoint3* outP = outPoints;

        for (int i = 0; i < 3; ++i) {
            int curr = idx[i];
            int next = idx[(i + 1) % 3];
            if (pts[curr].fZ > tol) {
                *outP++ = pts[curr];
                if (pts[next].fZ <= tol) { // curr is IN, next is OUT
                    *outP++ = clip(pts[curr], pts[next]);
                }
            } else {
                if (pts[next].fZ > tol) { // curr is OUT, next is IN
                    *outP++ = clip(pts[curr], pts[next]);
                }
            }
        }

        const int count = SkTo<int>(outP - outPoints);
        SkASSERT(count == 0 || count == 3 || count == 4);
        for (int i = 0; i < count; ++i) {
            float scale = 1.0f / outPoints[i].fZ;
            dst[i].set(outPoints[i].fX * scale, outPoints[i].fY * scale);
        }
        return count;
    };

    SkPoint tmp[kMaxClippedTrianglePointCount];
    int idx[] = { state.f0, state.f1, state.f2 };
    if (int n = clipTriangle(tmp, idx, dev3)) {
        // TODO: SkScan::FillConvexPoly(tmp, n, ...);
        SkASSERT(n == 3 || n == 4);
        SkScan::FillTriangle(tmp, rc, blitter);
        if (n == 4) {
            tmp[1] = tmp[2];
            tmp[2] = tmp[3];
            SkScan::FillTriangle(tmp, rc, blitter);
        }
    }
}
static void fill_triangle(const VertState& state, SkBlitter* blitter, const SkRasterClip& rc,
                          const SkPoint dev2[], const SkPoint3 dev3[]) {
    if (dev3) {
        fill_triangle_3(state, blitter, rc, dev3);
    } else {
        fill_triangle_2(state, blitter, rc, dev2);
    }
}

void SkDraw::drawFixedVertices(const SkVertices* vertices, SkBlendMode blendMode,
                               const SkPaint& paint, const SkMatrix& ctmInverse,
                               const SkPoint* dev2, const SkPoint3* dev3,
                               SkArenaAlloc* outerAlloc) const {
    SkVerticesPriv info(vertices->priv());

    const int vertexCount = info.vertexCount();
    const int indexCount = info.indexCount();
    const SkPoint* positions = info.positions();
    const SkPoint* textures = info.texCoords();
    const uint16_t* indices = info.indices();
    const SkColor* colors = info.colors();

    SkShader* shader = paint.getShader();
    if (shader) {
        if (!textures) {
            textures = positions;
        }
    } else {
        textures = nullptr;
    }

    // We can simplify things for certain blend modes. This is for speed, and SkComposeShader
    // itself insists we don't pass kSrc or kDst to it.
    if (colors && textures) {
        switch (blendMode) {
            case SkBlendMode::kSrc:
                colors = nullptr;
                break;
            case SkBlendMode::kDst:
                textures = nullptr;
                shader = nullptr;
                break;
            default: break;
        }
    }

    // There is a paintShader iff there is texCoords.
    SkASSERT((textures != nullptr) == (shader != nullptr));

    VertState       state(vertexCount, indices, indexCount);
    VertState::Proc vertProc = state.chooseProc(info.mode());
    // No colors are changing and no texture coordinates are changing, so no updates between
    // triangles are needed. Use SkVM to blit the triangles.
    if (!colors && (!textures || textures == positions)) {
        if (auto blitter = SkCreateSkVMBlitter(
                fDst, paint, *fMatrixProvider, outerAlloc, this->fRC->clipShader())) {
            while (vertProc(&state)) {
                fill_triangle(state, blitter, *fRC, dev2, dev3);
            }
            return;
        }
    }

    /*  We need to know if we have perspective or not, so we can know what stage(s) we will need,
        and how to prep our "uniforms" before each triangle in the tricolorshader.

        We could just check the matrix on each triangle to decide, but we have to be sure to always
        make the same decision, since we create 1 or 2 stages only once for the entire patch.

        To be safe, we just make that determination here, and pass it into the tricolorshader.
     */
    SkMatrix ctm = fMatrixProvider->localToDevice();
    const bool usePerspective = ctm.hasPerspective();

    SkTriColorShader* triShader = nullptr;
    SkPMColor4f*  dstColors = nullptr;

    if (colors) {
        dstColors = convert_colors(colors, vertexCount, fDst.colorSpace(), outerAlloc);
        triShader = outerAlloc->make<SkTriColorShader>(compute_is_opaque(colors, vertexCount),
                                                      usePerspective);
        if (shader) {
            shader = outerAlloc->make<SkShader_Blend>(blendMode,
                                                      sk_ref_sp(triShader), sk_ref_sp(shader));
        } else {
            shader = triShader;
        }
    }

    SkPaint shaderPaint(paint);
    shaderPaint.setShader(sk_ref_sp(shader));

    if (!textures) {    // only tricolor shader
        if (auto blitter = SkCreateRasterPipelineBlitter(
                fDst, shaderPaint, *fMatrixProvider, outerAlloc, this->fRC->clipShader())) {
            while (vertProc(&state)) {
                if (triShader &&
                    !triShader->update(ctmInverse, positions, dstColors,
                                       state.f0, state.f1, state.f2)) {
                    continue;
                }
                fill_triangle(state, blitter, *fRC, dev2, dev3);
            }
        }
        return;
    }

    SkRasterPipeline pipeline(outerAlloc);
    SkStageRec rec = {
            &pipeline,
            outerAlloc,
            fDst.colorType(),
            fDst.colorSpace(),
            shaderPaint,
            nullptr,
            *fMatrixProvider
    };
    if (auto updater = as_SB(shader)->appendUpdatableStages(rec)) {
        bool isOpaque = shader->isOpaque();
        if (triShader) {
            isOpaque = false;   // unless we want to walk all the colors, and see if they are
                                // all opaque (and the blend mode will keep them that way
        }

        // Positions as texCoords? The local matrix is always identity, so update once
        if (textures == positions) {
            SkMatrix localM;
            if (!updater->update(ctm, &localM)) {
                return;
            }
        }

        if (auto blitter = SkCreateRasterPipelineBlitter(
                fDst, shaderPaint, pipeline, isOpaque, outerAlloc, fRC->clipShader())) {
            while (vertProc(&state)) {
                if (triShader && !triShader->update(ctmInverse, positions, dstColors,
                                                    state.f0, state.f1, state.f2)) {
                    continue;
                }

                SkMatrix localM;
                if ((textures == positions) ||
                    (texture_to_matrix(state, positions, textures, &localM) &&
                     updater->update(ctm, &localM))) {
                    fill_triangle(state, blitter, *fRC, dev2, dev3);
                }
            }
        }
    } else {
        // must rebuild pipeline for each triangle, to pass in the computed ctm
        while (vertProc(&state)) {
            if (triShader && !triShader->update(ctmInverse, positions, dstColors,
                                                state.f0, state.f1, state.f2)) {
                continue;
            }

            SkSTArenaAlloc<2048> innerAlloc;

            const SkMatrixProvider* matrixProvider = fMatrixProvider;
            SkTLazy<SkPreConcatMatrixProvider> preConcatMatrixProvider;
            if (textures && (textures != positions)) {
                SkMatrix localM;
                if (!texture_to_matrix(state, positions, textures, &localM)) {
                    continue;
                }
                matrixProvider = preConcatMatrixProvider.init(*matrixProvider, localM);
            }

            if (auto blitter = SkCreateRasterPipelineBlitter(
                    fDst, shaderPaint, *matrixProvider, &innerAlloc, this->fRC->clipShader())) {
                fill_triangle(state, blitter, *fRC, dev2, dev3);
            }
        }
    }
}

void SkDraw::drawVertices(const SkVertices* vertices, SkBlendMode bmode,
                          const SkPaint& paint) const {
    SkVerticesPriv info(vertices->priv());
    const int vertexCount = info.vertexCount();
    const int indexCount = info.indexCount();

    // abort early if there is nothing to draw
    if (vertexCount < 3 || (indexCount > 0 && indexCount < 3) || fRC->isEmpty()) {
        return;
    }
    SkMatrix ctm = fMatrixProvider->localToDevice();
    SkMatrix ctmInv;
    if (!ctm.invert(&ctmInv)) {
        return;
    }

    constexpr size_t kDefVertexCount = 16;
    constexpr size_t kOuterSize = sizeof(SkTriColorShader) +
                                 sizeof(SkShader_Blend) +
                                 (2 * sizeof(SkPoint) + sizeof(SkColor4f)) * kDefVertexCount;
    SkSTArenaAlloc<kOuterSize> outerAlloc;

    SkPoint*  dev2 = nullptr;
    SkPoint3* dev3 = nullptr;

    if (ctm.hasPerspective()) {
        dev3 = outerAlloc.makeArray<SkPoint3>(vertexCount);
        ctm.mapHomogeneousPoints(dev3, info.positions(), vertexCount);
        // similar to the bounds check for 2d points (below)
        if (!SkScalarsAreFinite((const SkScalar*)dev3, vertexCount * 3)) {
            return;
        }
    } else {
        dev2 = outerAlloc.makeArray<SkPoint>(vertexCount);
        ctm.mapPoints(dev2, info.positions(), vertexCount);

        SkRect bounds;
        // this also sets bounds to empty if we see a non-finite value
        bounds.setBounds(dev2, vertexCount);
        if (bounds.isEmpty()) {
            return;
        }
    }

    this->drawFixedVertices(vertices, bmode, paint, ctmInv, dev2, dev3, &outerAlloc);
}