5c612ade3b
This sample attempts to re-create an image's alpha channel by drawing it one pixel at a time and timing how long each pixel takes to draw. The "abc" text should appear twice normally, and the third and fourth versions are reconstructed from timing, one by timing 1:1 pixel draws, the other by timing 1x1:1024x1024 upscale into an offscreen. It's not meant to be an exact reconstruction, but you can easily see the shapes, particularly at -O0, -O1, and -Os. Auto-vectorization from -O2/-O3 do a good amount to cover up the problem. The legacy CPU backend is the main place to look. I haven't been able to reconstruct any images using SkRasterPipelineBlitter or SkVMBlitter, and while on the GPU I do see non-random patterns in the timing, it appears to be the same single pattern across devices, OSes, GPUs, GPU APIs and content... I assume it's something like our resource caching policy. This can't really be a GM, given how it draws non-deterministically. Bug: chromium:1088224 Change-Id: I2ec79c8dd407ecb104fd9bf0c8039cb6dd1fe436 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/313466 Commit-Queue: Mike Klein <mtklein@google.com> Commit-Queue: Mike Reed <reed@google.com> Reviewed-by: Mike Reed <reed@google.com>
93 lines
3.2 KiB
C++
93 lines
3.2 KiB
C++
/*
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* Copyright 2020 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#include "include/core/SkCanvas.h"
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#include "include/core/SkFont.h"
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#include "include/core/SkSurface.h"
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#include "samplecode/Sample.h"
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#include <chrono>
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struct TimingSample : public Sample {
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static constexpr int W = 24,
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H = 16;
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sk_sp<SkImage> fImg;
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SkString name() override { return SkString("Timing"); }
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void onOnceBeforeDraw() override {
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sk_sp<SkSurface> surf = SkSurface::MakeRasterN32Premul(W,H);
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surf->getCanvas()->drawString("abc", 2,H-4, SkFont{}, SkPaint{});
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fImg = surf->makeImageSnapshot();
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}
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void onDrawContent(SkCanvas* canvas) override {
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canvas->scale(8,8);
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// Draw normally.
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canvas->drawImage(fImg, 0,0);
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canvas->translate(0,H);
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// Draw one pixel at a time with drawImageRect(),
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// timing how long each drawImageRect() call takes.
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double cost[H][W];
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double min = +INFINITY,
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max = -INFINITY;
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for (int y = 0; y < H; y++)
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for (int x = 0; x < W; x++) {
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auto start = std::chrono::steady_clock::now();
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canvas->drawImageRect(fImg, SkRect::MakeXYWH(x,y,1,1)
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, SkRect::MakeXYWH(x,y,1,1)
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, /*paint=*/nullptr);
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auto elapsed = std::chrono::steady_clock::now() - start;
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cost[y][x] = elapsed.count();
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min = std::min(min, cost[y][x]);
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max = std::max(max, cost[y][x]);
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}
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canvas->translate(0,H);
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// Draw using those per-pixel timings,
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// with the slowest pixel scaled to alpha=1, the fastest to alpha=0.
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for (int y = 0; y < H; y++)
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for (int x = 0; x < W; x++) {
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SkPaint p;
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p.setAlphaf( (cost[y][x] - min) / (max - min) );
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canvas->drawRect(SkRect::MakeXYWH(x,y,1,1), p);
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}
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canvas->translate(0,H);
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// Draw each pixel into offscreen, timing each draw.
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SkImageInfo info = canvas->imageInfo().makeWH(1024,1024);
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if (sk_sp<SkSurface> offscreen = canvas->makeSurface(info)) {
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min = +INFINITY;
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max = -INFINITY;
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for (int y = 0; y < H; y++)
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for (int x = 0; x < W; x++) {
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auto start = std::chrono::steady_clock::now();
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offscreen->getCanvas()->drawImageRect(fImg, SkRect::MakeXYWH(x,y,1,1)
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, SkRect::MakeXYWH(0,0,1024,1024)
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, /*paint=*/nullptr);
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auto elapsed = std::chrono::steady_clock::now() - start;
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cost[y][x] = elapsed.count();
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min = std::min(min, cost[y][x]);
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max = std::max(max, cost[y][x]);
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}
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for (int y = 0; y < H; y++)
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for (int x = 0; x < W; x++) {
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SkPaint p;
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p.setAlphaf( (cost[y][x] - min) / (max - min) );
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canvas->drawRect(SkRect::MakeXYWH(x,y,1,1), p);
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}
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}
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}
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};
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DEF_SAMPLE( return new TimingSample; )
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