src/gpu/ganesh/text/GaneshVertexFiller.cpp

/*
* Copyright 2025 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/

#include "src/text/gpu/VertexFiller.h"

#include "include/core/SkMatrix.h"
#include "include/core/SkPoint3.h"
#include "include/core/SkRect.h"
#include "include/core/SkScalar.h"
#include "include/private/base/SkAssert.h"
#include "include/private/base/SkPoint_impl.h"
#include "include/private/base/SkSpan_impl.h"
#include "src/base/SkZip.h"
#include "src/core/SkColorData.h"
#include "src/gpu/AtlasTypes.h"
#include "src/gpu/ganesh/GrColor.h"
#include "src/text/gpu/Glyph.h"

#include <cstddef>
#include <cstdint>
#include <tuple>

using MaskFormat = skgpu::MaskFormat;

namespace sktext::gpu {

struct AtlasPt {
    uint16_t u;
    uint16_t v;
};

// Normal text mask, SDFT, or color.
struct Mask2DVertex {
    SkPoint devicePos;
    GrColor color;
    AtlasPt atlasPos;
};

struct ARGB2DVertex {
    ARGB2DVertex(SkPoint d, GrColor, AtlasPt a) : devicePos{d}, atlasPos{a} {}

    SkPoint devicePos;
    AtlasPt atlasPos;
};

// Perspective SDFT or SDFT forced to 3D or perspective color.
struct Mask3DVertex {
    SkPoint3 devicePos;
    GrColor color;
    AtlasPt atlasPos;
};

struct ARGB3DVertex {
    ARGB3DVertex(SkPoint3 d, GrColor, AtlasPt a) : devicePos{d}, atlasPos{a} {}

    SkPoint3 devicePos;
    AtlasPt atlasPos;
};

size_t VertexFiller::vertexStride(const SkMatrix &matrix) const {
    if (fMaskType != skgpu::MaskFormat::kARGB) {
        // For formats MaskFormat::kA565 and MaskFormat::kA8 where A8 include SDF.
        return matrix.hasPerspective() ? sizeof(Mask3DVertex) : sizeof(Mask2DVertex);
    } else {
        // For format MaskFormat::kARGB
        return matrix.hasPerspective() ? sizeof(ARGB3DVertex) : sizeof(ARGB2DVertex);
    }
}

// The 99% case. Direct Mask, No clip, No RGB.
void fillDirectNoClipping(SkZip<Mask2DVertex[4], const Glyph*, const SkPoint> quadData,
                          GrColor color,
                          SkPoint originOffset) {
    for (auto[quad, glyph, leftTop] : quadData) {
        auto[al, at, ar, ab] = glyph->fAtlasLocator.getUVs();
        SkScalar dl = leftTop.x() + originOffset.x(),
                 dt = leftTop.y() + originOffset.y(),
                 dr = dl + (ar - al),
                 db = dt + (ab - at);

        quad[0] = {{dl, dt}, color, {al, at}};  // L,T
        quad[1] = {{dl, db}, color, {al, ab}};  // L,B
        quad[2] = {{dr, dt}, color, {ar, at}};  // R,T
        quad[3] = {{dr, db}, color, {ar, ab}};  // R,B
    }
}

template <typename Rect>
static auto LTBR(const Rect& r) {
    return std::make_tuple(r.left(), r.top(), r.right(), r.bottom());
}

// Handle any combination of BW or color and clip or no clip.
template<typename Quad, typename VertexData>
static void fillDirectClipped(SkZip<Quad, const Glyph*, const VertexData> quadData,
                              GrColor color,
                              SkPoint originOffset,
                              SkIRect* clip = nullptr) {
    for (auto[quad, glyph, leftTop] : quadData) {
        auto[al, at, ar, ab] = glyph->fAtlasLocator.getUVs();
        uint16_t w = ar - al,
                 h = ab - at;
        SkScalar l = leftTop.x() + originOffset.x(),
                 t = leftTop.y() + originOffset.y();
        if (clip == nullptr) {
            auto[dl, dt, dr, db] = SkRect::MakeLTRB(l, t, l + w, t + h);
            quad[0] = {{dl, dt}, color, {al, at}};  // L,T
            quad[1] = {{dl, db}, color, {al, ab}};  // L,B
            quad[2] = {{dr, dt}, color, {ar, at}};  // R,T
            quad[3] = {{dr, db}, color, {ar, ab}};  // R,B
        } else {
            SkIRect devIRect = SkIRect::MakeLTRB(l, t, l + w, t + h);
            SkScalar dl, dt, dr, db;
            if (!clip->containsNoEmptyCheck(devIRect)) {
                if (SkIRect clipped; clipped.intersect(devIRect, *clip)) {
                    al += clipped.left()   - devIRect.left();
                    at += clipped.top()    - devIRect.top();
                    ar += clipped.right()  - devIRect.right();
                    ab += clipped.bottom() - devIRect.bottom();
                    std::tie(dl, dt, dr, db) = LTBR(clipped);
                } else {
                    // TODO: omit generating any vertex data for fully clipped glyphs ?
                    std::tie(dl, dt, dr, db) = std::make_tuple(0, 0, 0, 0);
                    std::tie(al, at, ar, ab) = std::make_tuple(0, 0, 0, 0);
                }
            } else {
                std::tie(dl, dt, dr, db) = LTBR(devIRect);
            }
            quad[0] = {{dl, dt}, color, {al, at}};  // L,T
            quad[1] = {{dl, db}, color, {al, ab}};  // L,B
            quad[2] = {{dr, dt}, color, {ar, at}};  // R,T
            quad[3] = {{dr, db}, color, {ar, ab}};  // R,B
        }
    }
}

template<typename Quad, typename VertexData>
static void fill2D(SkZip<Quad, const Glyph*, const VertexData> quadData,
                   GrColor color,
                   const SkMatrix& viewDifference) {
    for (auto [quad, glyph, leftTop] : quadData) {
        auto [l, t] = leftTop;
        auto [r, b] = leftTop + glyph->fAtlasLocator.widthHeight();
        SkPoint lt = viewDifference.mapPoint({l, t}),
                lb = viewDifference.mapPoint({l, b}),
                rt = viewDifference.mapPoint({r, t}),
                rb = viewDifference.mapPoint({r, b});
        auto [al, at, ar, ab] = glyph->fAtlasLocator.getUVs();
        quad[0] = {lt, color, {al, at}};  // L,T
        quad[1] = {lb, color, {al, ab}};  // L,B
        quad[2] = {rt, color, {ar, at}};  // R,T
        quad[3] = {rb, color, {ar, ab}};  // R,B
    }
}

template<typename Quad, typename VertexData>
static void fill3D(SkZip<Quad, const Glyph*, const VertexData> quadData,
                   GrColor color,
                   const SkMatrix& viewDifference) {
    auto mapXYZ = [&](SkScalar x, SkScalar y) {
        return viewDifference.mapPointToHomogeneous({x, y});
    };
    for (auto [quad, glyph, leftTop] : quadData) {
        auto [l, t] = leftTop;
        auto [r, b] = leftTop + glyph->fAtlasLocator.widthHeight();
        SkPoint3 lt = mapXYZ(l, t),
                lb = mapXYZ(l, b),
                rt = mapXYZ(r, t),
                rb = mapXYZ(r, b);
        auto [al, at, ar, ab] = glyph->fAtlasLocator.getUVs();
        quad[0] = {lt, color, {al, at}};  // L,T
        quad[1] = {lb, color, {al, ab}};  // L,B
        quad[2] = {rt, color, {ar, at}};  // R,T
        quad[3] = {rb, color, {ar, ab}};  // R,B
    }
}

void VertexFiller::fillVertexData(int offset, int count,
                                  SkSpan<const Glyph*> glyphs,
                                  const SkPMColor4f& pmColor,
                                  const SkMatrix& positionMatrix,
                                  SkIRect clip,
                                  void* vertexBuffer) const {
    GrColor color = pmColor.toBytes_RGBA();
    auto quadData = [&](auto dst) {
        return SkMakeZip(dst,
                         glyphs.subspan(offset, count),
                         fLeftTop.subspan(offset, count));
    };

    // Handle direct mask drawing specifically.
    if (fCanDrawDirect) {
        auto [noTransformNeeded, originOffset] = CanUseDirect(fCreationMatrix, positionMatrix);

        if (noTransformNeeded) {
            if (clip.isEmpty()) {
                if (fMaskType != MaskFormat::kARGB) {
                    using Quad = Mask2DVertex[4];
                    SkASSERT(sizeof(Mask2DVertex) == this->vertexStride(SkMatrix::I()));
                    fillDirectNoClipping(quadData((Quad*)vertexBuffer), color, originOffset);
                } else {
                    using Quad = ARGB2DVertex[4];
                    SkASSERT(sizeof(ARGB2DVertex) == this->vertexStride(SkMatrix::I()));
                    fillDirectClipped(quadData((Quad*)vertexBuffer), color, originOffset);
                }
            } else {
                if (fMaskType != MaskFormat::kARGB) {
                    using Quad = Mask2DVertex[4];
                    SkASSERT(sizeof(Mask2DVertex) == this->vertexStride(SkMatrix::I()));
                    fillDirectClipped(quadData((Quad*)vertexBuffer), color, originOffset, &clip);
                } else {
                    using Quad = ARGB2DVertex[4];
                    SkASSERT(sizeof(ARGB2DVertex) == this->vertexStride(SkMatrix::I()));
                    fillDirectClipped(quadData((Quad*)vertexBuffer), color, originOffset, &clip);
                }
            }
            return;
        }
    }

    // Handle the general transformed case.
    SkMatrix viewDifference = this->viewDifference(positionMatrix);
    if (!positionMatrix.hasPerspective()) {
        if (fMaskType == MaskFormat::kARGB) {
            using Quad = ARGB2DVertex[4];
            SkASSERT(sizeof(ARGB2DVertex) == this->vertexStride(positionMatrix));
            fill2D(quadData((Quad*)vertexBuffer), color, viewDifference);
        } else {
            using Quad = Mask2DVertex[4];
            SkASSERT(sizeof(Mask2DVertex) == this->vertexStride(positionMatrix));
            fill2D(quadData((Quad*)vertexBuffer), color, viewDifference);
        }
    } else {
        if (fMaskType == MaskFormat::kARGB) {
            using Quad = ARGB3DVertex[4];
            SkASSERT(sizeof(ARGB3DVertex) == this->vertexStride(positionMatrix));
            fill3D(quadData((Quad*)vertexBuffer), color, viewDifference);
        } else {
            using Quad = Mask3DVertex[4];
            SkASSERT(sizeof(Mask3DVertex) == this->vertexStride(positionMatrix));
            fill3D(quadData((Quad*)vertexBuffer), color, viewDifference);
        }
    }
}

}  // namespace sktext::gpu