src/gpu/batches/GrNonAAStrokeRectBatch.cpp

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "GrNonAAStrokeRectBatch.h"

#include "GrBatchTest.h"
#include "GrBatchFlushState.h"
#include "GrColor.h"
#include "GrDefaultGeoProcFactory.h"
#include "GrVertexBatch.h"
#include "SkRandom.h"

/*  create a triangle strip that strokes the specified rect. There are 8
    unique vertices, but we repeat the last 2 to close up. Alternatively we
    could use an indices array, and then only send 8 verts, but not sure that
    would be faster.
    */
static void init_stroke_rect_strip(SkPoint verts[10], const SkRect& rect, SkScalar width) {
    const SkScalar rad = SkScalarHalf(width);
    // TODO we should be able to enable this assert, but we'd have to filter these draws
    // this is a bug
    //SkASSERT(rad < rect.width() / 2 && rad < rect.height() / 2);

    verts[0].set(rect.fLeft + rad, rect.fTop + rad);
    verts[1].set(rect.fLeft - rad, rect.fTop - rad);
    verts[2].set(rect.fRight - rad, rect.fTop + rad);
    verts[3].set(rect.fRight + rad, rect.fTop - rad);
    verts[4].set(rect.fRight - rad, rect.fBottom - rad);
    verts[5].set(rect.fRight + rad, rect.fBottom + rad);
    verts[6].set(rect.fLeft + rad, rect.fBottom - rad);
    verts[7].set(rect.fLeft - rad, rect.fBottom + rad);
    verts[8] = verts[0];
    verts[9] = verts[1];
}

// Allow all hairlines and all miters, so long as the miter limit doesn't produce beveled corners.
inline static bool allowed_stroke(const SkStrokeRec& stroke) {
    SkASSERT(stroke.getStyle() == SkStrokeRec::kStroke_Style ||
             stroke.getStyle() == SkStrokeRec::kHairline_Style);
    return !stroke.getWidth() ||
           (stroke.getJoin() == SkPaint::kMiter_Join && stroke.getMiter() > SK_ScalarSqrt2);
}

class NonAAStrokeRectBatch : public GrVertexBatch {
public:
    DEFINE_BATCH_CLASS_ID

    const char* name() const override { return "NonAAStrokeRectBatch"; }

    void computePipelineOptimizations(GrInitInvariantOutput* color,
                                      GrInitInvariantOutput* coverage,
                                      GrBatchToXPOverrides* overrides) const override {
        // When this is called on a batch, there is only one geometry bundle
        color->setKnownFourComponents(fColor);
        coverage->setKnownSingleComponent(0xff);
    }

    static GrDrawBatch* Create(GrColor color, const SkMatrix& viewMatrix, const SkRect& rect,
                               const SkStrokeRec& stroke, bool snapToPixelCenters) {
        if (!allowed_stroke(stroke)) {
            return nullptr;
        }
        NonAAStrokeRectBatch* batch = new NonAAStrokeRectBatch();
        batch->fColor = color;
        batch->fViewMatrix = viewMatrix;
        batch->fRect = rect;
        // Sort the rect for hairlines
        batch->fRect.sort();
        batch->fStrokeWidth = stroke.getWidth();

        SkScalar rad = SkScalarHalf(batch->fStrokeWidth);
        SkRect bounds = rect;
        bounds.outset(rad, rad);

        // If our caller snaps to pixel centers then we have to round out the bounds
        if (snapToPixelCenters) {
            viewMatrix.mapRect(&bounds);
            // We want to be consistent with how we snap non-aa lines. To match what we do in
            // GrGLSLVertexShaderBuilder, we first floor all the vertex values and then add half a
            // pixel to force us to pixel centers.
            bounds.set(SkScalarFloorToScalar(bounds.fLeft),
                       SkScalarFloorToScalar(bounds.fTop),
                       SkScalarFloorToScalar(bounds.fRight),
                       SkScalarFloorToScalar(bounds.fBottom));
            bounds.offset(0.5f, 0.5f);
            batch->setBounds(bounds, HasAABloat::kNo, IsZeroArea::kNo);
        } else {
            batch->setTransformedBounds(bounds, batch->fViewMatrix, HasAABloat ::kNo,
                                        IsZeroArea::kNo);
        }
        return batch;
    }

private:
    NonAAStrokeRectBatch() : INHERITED(ClassID()) {}

    void onPrepareDraws(Target* target) const override {
        sk_sp<GrGeometryProcessor> gp;
        {
            using namespace GrDefaultGeoProcFactory;
            Color color(fColor);
            Coverage coverage(fOverrides.readsCoverage() ? Coverage::kSolid_Type
                                                         : Coverage::kNone_Type);
            LocalCoords localCoords(fOverrides.readsLocalCoords() ? LocalCoords::kUsePosition_Type :
                                                                    LocalCoords::kUnused_Type);
            gp = GrDefaultGeoProcFactory::Make(color, coverage, localCoords, fViewMatrix);
        }

        size_t vertexStride = gp->getVertexStride();

        SkASSERT(vertexStride == sizeof(GrDefaultGeoProcFactory::PositionAttr));

        int vertexCount = kVertsPerHairlineRect;
        if (fStrokeWidth > 0) {
            vertexCount = kVertsPerStrokeRect;
        }

        const GrBuffer* vertexBuffer;
        int firstVertex;

        void* verts = target->makeVertexSpace(vertexStride, vertexCount, &vertexBuffer,
                                              &firstVertex);

        if (!verts) {
            SkDebugf("Could not allocate vertices\n");
            return;
        }

        SkPoint* vertex = reinterpret_cast<SkPoint*>(verts);

        GrPrimitiveType primType;
        if (fStrokeWidth > 0) {
            primType = kTriangleStrip_GrPrimitiveType;
            init_stroke_rect_strip(vertex, fRect, fStrokeWidth);
        } else {
            // hairline
            primType = kLineStrip_GrPrimitiveType;
            vertex[0].set(fRect.fLeft, fRect.fTop);
            vertex[1].set(fRect.fRight, fRect.fTop);
            vertex[2].set(fRect.fRight, fRect.fBottom);
            vertex[3].set(fRect.fLeft, fRect.fBottom);
            vertex[4].set(fRect.fLeft, fRect.fTop);
        }

        GrMesh mesh;
        mesh.init(primType, vertexBuffer, firstVertex, vertexCount);
        target->draw(gp.get(), mesh);
    }

    void initBatchTracker(const GrXPOverridesForBatch& overrides) override {
        overrides.getOverrideColorIfSet(&fColor);
        fOverrides = overrides;
    }

    bool onCombineIfPossible(GrBatch* t, const GrCaps&) override {
        // NonAA stroke rects cannot batch right now
        // TODO make these batchable
        return false;
    }

    GrColor fColor;
    SkMatrix fViewMatrix;
    SkRect fRect;
    SkScalar fStrokeWidth;

    GrXPOverridesForBatch fOverrides;

    const static int kVertsPerHairlineRect = 5;
    const static int kVertsPerStrokeRect = 10;


    typedef GrVertexBatch INHERITED;
};

namespace GrNonAAStrokeRectBatch {

GrDrawBatch* Create(GrColor color,
                    const SkMatrix& viewMatrix,
                    const SkRect& rect,
                    const SkStrokeRec& stroke,
                    bool snapToPixelCenters) {
    return NonAAStrokeRectBatch::Create(color, viewMatrix, rect, stroke, snapToPixelCenters);
}

}

#ifdef GR_TEST_UTILS

DRAW_BATCH_TEST_DEFINE(NonAAStrokeRectBatch) {
    SkMatrix viewMatrix = GrTest::TestMatrix(random);
    GrColor color = GrRandomColor(random);
    SkRect rect = GrTest::TestRect(random);
    SkScalar strokeWidth = random->nextBool() ? 0.0f : 2.0f;
    SkPaint paint;
    paint.setStrokeWidth(strokeWidth);
    paint.setStyle(SkPaint::kStroke_Style);
    paint.setStrokeJoin(SkPaint::kMiter_Join);
    SkStrokeRec strokeRec(paint);
    return GrNonAAStrokeRectBatch::Create(color, viewMatrix, rect, strokeRec, random->nextBool());
}

#endif