Fix the way we patch up the matrix for scaled images that aren't

gm/tiledscaledbitmap.cpp

Index: gm/tiledscaledbitmap.cpp
diff --git a/gm/tiledscaledbitmap.cpp b/gm/tiledscaledbitmap.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..78f2d389d1054467e7fd68417aba965d1f2b2440
--- /dev/null
+++ b/gm/tiledscaledbitmap.cpp
@@ -0,0 +1,93 @@
+
+/*
+ * 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 "gm.h"
+
+#include "Resources.h"
+#include "SkBitmap.h"
+#include "SkImageDecoder.h"
+#include "SkPaint.h"
+#include "SkShader.h"
+#include "SkStream.h"
+
+
+ /***
+  *
+  * This GM reproduces Skia bug 2904, in which a tiled bitmap shader was failing to draw correctly
+  * when fractional image scaling was ignored by the high quality bitmap scaler.
+  *
+  ***/
+
+namespace skiagm {
+
+class TiledScaledBitmapGM : public GM {
+public:
+
+    TiledScaledBitmapGM(const char filename[])
+      : fFilename(filename) {
+    }
+
+protected:
+    virtual SkString onShortName() {
+        return SkString("tiledscaledbitmap");
+    }
+
+    virtual SkISize onISize() {
+        return SkISize::Make(1016, 616);
+    }
+
+    virtual void onOnceBeforeDraw() SK_OVERRIDE {
+        SkImageDecoder* codec = NULL;
+        SkString resourcePath = GetResourcePath(fFilename.c_str());

[reed1, 2014/10/24 14:27:38]

I think it is just as easy (and slightly more portable/tweakable) to just
generate the bitmap in code. That makes it trivial to create variations of the
test as desired in the future (e.g. images w/ or w/o per-pixel alpha, images in
different bit-depths, images that are small, large, pow-of-2, etc.).

Many of our GMs already do this (grep for make_bitmap or make_bm)

e.g.

static SkImage* make_image(...) {
    SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
    SkPaint paint;
    surface->getCanvas()->drawCircle(..., paint);
    return surface->newImageSnapshot();
}

static SkBitmap make_bitmap(...) {
    SkBitmap bm;
    bm.allocPixels(info);
    SkCanvas canvas(bm);
    SkPaint paint;
    canvas.drawCircle(..., paint);
    return bm;
}

+        SkFILEStream stream(resourcePath.c_str());
+        if (stream.isValid()) {
+            codec = SkImageDecoder::Factory(&stream);
+        }
+        if (codec) {
+            stream.rewind();
+            codec->decode(&stream, &fBitmap, kN32_SkColorType, SkImageDecoder::kDecodePixels_Mode);
+            SkDELETE(codec);
+        } else {
+            fBitmap.allocN32Pixels(360,288);
+            for (int row = 0 ; row < 288 ; row++) {
+                for (int col = 0 ; col < 360 ; col++ ) {
+                    *(fBitmap.getAddr32(row,col)) = 0xFF0000FF; // red == bad
+                }
+            }
+        }
+    }
+
+    virtual void onDraw(SkCanvas* canvas) {
+        SkPaint paint;
+
+        paint.setAntiAlias(true);
+        paint.setFilterLevel(SkPaint::kHigh_FilterLevel);
+
+        SkMatrix mat;
+        mat.setScale(121.f/360.f, 93.f/288.f);
+        mat.postTranslate(-72, -72);
+
+        SkShader *shader = SkShader::CreateBitmapShader(fBitmap, SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode, &mat);
+        paint.setShader(shader);
+
+        SkSafeUnref(shader);
+        canvas->drawRectCoords(8,8,1008, 608, paint);
+    }
+
+private:
+    SkBitmap fBitmap;
+    SkString fFilename;
+
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* MyFactory(void*) { return new TiledScaledBitmapGM("circle.png"); }

[reed1, 2014/10/24 14:27:38]

nit: DEF_GM( return SkNEW_ARGS(TiledScaledBitmapGM, (...) ); )

[humper, 2014/10/24 15:10:01]

Done.

+static GMRegistry reg(MyFactory);
+
+}