docs/examples/Bitmap_readPixels.cpp

// Copyright 2019 Google LLC
// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
#include "tools/fiddle/examples.h"
REG_FIDDLE(Bitmap_readPixels, 256, 128, false, 0) {
void draw(SkCanvas* canvas) {
    const int width = 256;
    const int height = 64;
    SkImageInfo srcInfo = SkImageInfo::MakeN32Premul(width, height);
    const SkColor4f colors[] = { SkColors::kRed, SkColors::kBlue.withAlpha(0.5f) };
    const SkPoint   points[] = { { 0, 0 }, { 256, 0 } };
    SkPaint paint;
    paint.setShader(SkShaders::LinearGradient(points, {{colors, {}, SkTileMode::kClamp}, {}}));
    SkBitmap bitmap;
    bitmap.allocPixels(srcInfo);
    SkCanvas srcCanvas(bitmap);
    srcCanvas.drawRect(SkRect::MakeWH(width, height), paint);
    canvas->drawImage(bitmap.asImage(), 0, 0);
    SkImageInfo dstInfo = srcInfo.makeColorType(kARGB_4444_SkColorType);
    std::vector<int16_t> dstPixels;
    dstPixels.resize(height * width);
    bitmap.readPixels(dstInfo, &dstPixels.front(), width * 2, 0, 0);
    SkPixmap dstPixmap(dstInfo, &dstPixels.front(), width * 2);
    bitmap.installPixels(dstPixmap);
    canvas->drawImage(bitmap.asImage(), 0, 64);
}
}  // END FIDDLE