gm/discard.cpp

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkCanvas.h"
#include "SkPaint.h"
#include "SkRandom.h"
#include "SkSurface.h"
#include "ToolUtils.h"
#include "gm.h"

namespace skiagm {

/*
 * This GM exercises SkCanvas::discard() by creating an offscreen SkSurface and repeatedly
 * discarding it, drawing to it, and then drawing it to the main canvas.
 */
class DiscardGM : public GpuGM {

public:
    DiscardGM() {
    }

protected:
    SkString onShortName() override {
        return SkString("discard");
    }

    SkISize onISize() override {
        return SkISize::Make(100, 100);
    }

    DrawResult onDraw(GrContext* context, GrRenderTargetContext*, SkCanvas* canvas,
                      SkString* errorMsg) override {
        SkISize size = this->getISize();
        size.fWidth /= 10;
        size.fHeight /= 10;
        SkImageInfo info = SkImageInfo::MakeN32Premul(size);
        auto surface = SkSurface::MakeRenderTarget(context, SkBudgeted::kNo, info);
        if (nullptr == surface) {
            *errorMsg = "Could not create render target.";
            return DrawResult::kFail;
        }

        canvas->clear(SK_ColorBLACK);

        SkRandom rand;
        for (int x = 0; x < 10; ++x) {
            for (int y = 0; y < 10; ++y) {
              surface->getCanvas()->discard();
              // Make something that isn't too close to the background color, black.
              SkColor color = ToolUtils::color_to_565(rand.nextU() | 0xFF404040);
              switch (rand.nextULessThan(3)) {
                  case 0:
                      surface->getCanvas()->drawColor(color);
                      break;
                  case 1:
                      surface->getCanvas()->clear(color);
                      break;
                  case 2:
                      SkPaint paint;
                      paint.setShader(SkShaders::Color(color));
                      surface->getCanvas()->drawPaint(paint);
                      break;
              }
              surface->draw(canvas, 10.f*x, 10.f*y, nullptr);
            }
        }

        surface->getCanvas()->discard();
        return DrawResult::kOk;
    }

private:
    typedef GM INHERITED;
};

//////////////////////////////////////////////////////////////////////////////

DEF_GM(return new DiscardGM;)

} // end namespace