API to support native scaling by image-generator

gm/image.cpp

Index: gm/image.cpp
diff --git a/gm/image.cpp b/gm/image.cpp
index 991b4014f02aa3bfff0a2a3126a29f5210a21591..ac72f63b36f96dc2ab271778578d9e31a588b35e 100644
--- a/gm/image.cpp
+++ b/gm/image.cpp
@@ -240,33 +240,33 @@ static void draw_contents(SkCanvas* canvas) {
     canvas->drawCircle(50, 50, 35, paint);
 }
 
-static SkImage* make_raster(const SkImageInfo& info, GrContext*) {
+static SkImage* make_raster(const SkImageInfo& info, GrContext*, void (*draw)(SkCanvas*)) {
     SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
-    draw_contents(surface->getCanvas());
+    draw(surface->getCanvas());
     return surface->newImageSnapshot();
 }
 
-static SkImage* make_picture(const SkImageInfo& info, GrContext*) {
+static SkImage* make_picture(const SkImageInfo& info, GrContext*, void (*draw)(SkCanvas*)) {
     SkPictureRecorder recorder;
-    draw_contents(recorder.beginRecording(SkRect::MakeIWH(info.width(), info.height())));
+    draw(recorder.beginRecording(SkRect::MakeIWH(info.width(), info.height())));
     SkAutoTUnref<SkPicture> pict(recorder.endRecording());
     return SkImage::NewFromPicture(pict, info.dimensions(), nullptr, nullptr);
 }
 
-static SkImage* make_codec(const SkImageInfo& info, GrContext*) {
-    SkAutoTUnref<SkImage> image(make_raster(info, nullptr));
+static SkImage* make_codec(const SkImageInfo& info, GrContext*, void (*draw)(SkCanvas*)) {
+    SkAutoTUnref<SkImage> image(make_raster(info, nullptr, draw));
     SkAutoTUnref<SkData> data(image->encode());
     return SkImage::NewFromEncoded(data);
 }
 
-static SkImage* make_gpu(const SkImageInfo& info, GrContext* ctx) {
+static SkImage* make_gpu(const SkImageInfo& info, GrContext* ctx, void (*draw)(SkCanvas*)) {
     if (!ctx) { return nullptr; }
     SkAutoTUnref<SkSurface> surface(SkSurface::NewRenderTarget(ctx, SkSurface::kNo_Budgeted, info));
-    draw_contents(surface->getCanvas());
+    draw(surface->getCanvas());
     return surface->newImageSnapshot();
 }
 
-typedef SkImage* (*ImageMakerProc)(const SkImageInfo&, GrContext*);
+typedef SkImage* (*ImageMakerProc)(const SkImageInfo&, GrContext*, void (*)(SkCanvas*));
 
 class ScalePixelsGM : public skiagm::GM {
 public:
@@ -288,7 +288,7 @@ protected:
             make_codec, make_raster, make_picture, make_codec, make_gpu,
         };
         for (auto& proc : procs) {
-            SkAutoTUnref<SkImage> image(proc(info, canvas->getGrContext()));
+            SkAutoTUnref<SkImage> image(proc(info, canvas->getGrContext(), draw_contents));
             if (image) {
                 show_scaled_pixels(canvas, image);
             }
@@ -300,3 +300,132 @@ private:
     typedef skiagm::GM INHERITED;
 };
 DEF_GM( return new ScalePixelsGM; )
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+#include "SkImageGenerator.h"
+
+static SkImageInfo make_info(SkImage* img) {
+    return SkImageInfo::MakeN32(img->width(), img->height(),
+                                img->isOpaque() ? kOpaque_SkAlphaType : kPremul_SkAlphaType);
+}
+
+// Its simple, but I wonder if we should expose this formally?
+//
+class ImageGeneratorFromImage : public SkImageGenerator {
+public:
+    ImageGeneratorFromImage(SkImage* img) : INHERITED(make_info(img)), fImg(SkRef(img)) {}
+
+protected:
+    bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, SkPMColor ctable[],
+                     int* ctableCount) override {
+        return fImg->readPixels(info, pixels, rowBytes, 0, 0);
+    }
+
+private:
+    SkAutoTUnref<SkImage> fImg;
+
+    typedef SkImageGenerator INHERITED;
+};
+
+static void draw_opaque_contents(SkCanvas* canvas) {
+    canvas->drawColor(0xFFFF8844);
+
+    SkPaint paint;
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setStrokeWidth(20);
+    canvas->drawCircle(50, 50, 35, paint);
+}
+
+static SkImageGenerator* gen_raster(const SkImageInfo& info) {
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
+    draw_opaque_contents(surface->getCanvas());
+    SkAutoTUnref<SkImage> img(surface->newImageSnapshot());
+    return new ImageGeneratorFromImage(img);
+}
+
+static SkImageGenerator* gen_picture(const SkImageInfo& info) {
+    SkPictureRecorder recorder;
+    draw_opaque_contents(recorder.beginRecording(SkRect::MakeIWH(info.width(), info.height())));
+    SkAutoTUnref<SkPicture> pict(recorder.endRecording());
+    return SkImageGenerator::NewFromPicture(info.dimensions(), pict, nullptr, nullptr);
+}
+
+static SkImageGenerator* gen_png(const SkImageInfo& info) {
+    SkAutoTUnref<SkImage> image(make_raster(info, nullptr, draw_opaque_contents));
+    SkAutoTUnref<SkData> data(image->encode(SkImageEncoder::kPNG_Type, 100));
+    return SkImageGenerator::NewFromEncoded(data);
+}
+
+static SkImageGenerator* gen_jpg(const SkImageInfo& info) {
+    SkAutoTUnref<SkImage> image(make_raster(info, nullptr, draw_opaque_contents));
+    SkAutoTUnref<SkData> data(image->encode(SkImageEncoder::kJPEG_Type, 100));
+    return SkImageGenerator::NewFromEncoded(data);
+}
+
+typedef SkImageGenerator* (*GeneratorMakerProc)(const SkImageInfo&);
+
+static void show_scaled_generator(SkCanvas* canvas, SkImageGenerator* gen) {
+    const SkImageInfo genInfo = gen->getInfo();
+
+    SkAutoCanvasRestore acr(canvas, true);
+
+    SkBitmap bm;
+    bm.allocPixels(genInfo);
+    if (gen->getPixels(bm.info(), bm.getPixels(), bm.rowBytes())) {
+        canvas->drawBitmap(bm, 0, 0, nullptr);
+    }
+    canvas->translate(110, 0);
+
+    const float scales[] = { 0.75f, 0.5f, 0.25f };
+    for (auto scale : scales) {
+        SkImageGenerator::SupportedSizes sizes;
+        if (gen->computeScaledDimensions(scale, &sizes)) {
+            const SkImageInfo info = SkImageInfo::MakeN32Premul(sizes.fSizes[0].width(),
+                                                                sizes.fSizes[0].height());
+            bm.allocPixels(info);
+            SkPixmap pmap;
+            bm.peekPixels(&pmap);
+            if (gen->generateScaledPixels(pmap)) {
+                canvas->drawBitmap(bm, 0, SkIntToScalar(genInfo.height() - info.height())/2);
+            }
+        }
+        canvas->translate(100, 0);
+    }
+}
+
+class ScaleGeneratorGM : public skiagm::GM {
+public:
+    ScaleGeneratorGM() {}
+
+protected:
+    SkString onShortName() override {
+        return SkString("scale-generator");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(500, 500);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        canvas->translate(10, 10);
+
+        // explicitly make it opaque, so we can test JPEG (which is only ever opaque)
+        const SkImageInfo info = SkImageInfo::MakeN32(100, 100, kOpaque_SkAlphaType);
+
+        const GeneratorMakerProc procs[] = {
+            gen_raster, gen_picture, gen_png, gen_jpg,
+        };
+        for (auto& proc : procs) {
+            SkAutoTDelete<SkImageGenerator> gen(proc(info));
+            if (gen) {
+                show_scaled_generator(canvas, gen);
+            }
+            canvas->translate(0, 120);
+        }
+    }
+
+private:
+    typedef skiagm::GM INHERITED;
+};
+DEF_GM( return new ScaleGeneratorGM; )