Use texture size to determine precision of texture coord varyings

gm/tallstretchedbitmaps.cpp

Index: gm/tallstretchedbitmaps.cpp
diff --git a/gm/tallstretchedbitmaps.cpp b/gm/tallstretchedbitmaps.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..905cee8c652cda754d3e3f7408278fd349df3ddc
--- /dev/null
+++ b/gm/tallstretchedbitmaps.cpp
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+/*
+ * 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 "SkCanvas.h"
+#include "SkGradientShader.h"
+#include "SkPath.h"
+#include "SkRandom.h"
+
+int make_bm(SkBitmap* bm, int height) {
+    static const int kRadius = 22;
+    static const int kMargin = 8;
+    static const SkScalar kStartAngle = 0;
+    static const SkScalar kDAngle = 25;
+    static const SkScalar kSweep = 320;
+    static const SkScalar kThickness = 8;
+
+    int count = (height / (2 * kRadius + kMargin));
+    height = count * (2 * kRadius + kMargin);
+
+    bm->allocN32Pixels(2 * (kRadius + kMargin), height);
+    SkRandom random;
+
+    SkCanvas wholeCanvas(*bm);
+    wholeCanvas.clear(0x00000000);
+
+    SkScalar angle = kStartAngle;
+    for (int i = 0; i < count; ++i) {
+        SkPaint paint;
+        // The sw rasterizer disables AA for large canvii. So we make a small canvas for each draw.
+        SkBitmap smallBM;
+        SkIRect subRect = SkIRect::MakeXYWH(0, i * (kMargin + 2 * kRadius),
+                                            2 * kRadius + kMargin, 2 * kRadius + kMargin);
+        bm->extractSubset(&smallBM, subRect);
+        SkCanvas canvas(smallBM);
+        canvas.translate(kMargin + kRadius, kMargin + kRadius);
+
+        paint.setAntiAlias(true);
+        paint.setColor(random.nextU() | 0xFF000000);
+        paint.setStyle(SkPaint::kStroke_Style);
+        paint.setStrokeWidth(kThickness);
+        paint.setStrokeCap(SkPaint::kRound_Cap);
+        SkScalar radius = kRadius - kThickness / 2;
+        SkRect bounds = SkRect::MakeLTRB(-radius, -radius, radius, radius);
+
+        canvas.drawArc(bounds, angle, kSweep, false, paint);
+        angle += kDAngle;
+    }
+    bm->setImmutable();
+    return count;
+}
+
+class TallStretchedBitmapsGM : public skiagm::GM {
+public:
+    TallStretchedBitmapsGM() {}
+
+protected:
+    SkString onShortName() SK_OVERRIDE {
+        return SkString("tall_stretched_bitmaps");
+    }
+
+    SkISize onISize() SK_OVERRIDE {
+        return SkISize::Make(750, 750);
+    }
+
+    void onOnceBeforeDraw() SK_OVERRIDE {
+        for (size_t i = 0; i < SK_ARRAY_COUNT(fTallBmps); ++i) {
+            int h = (4 + i) * 1024;
+
+            fTallBmps[i].fItemCnt = make_bm(&fTallBmps[i].fBmp, h);
+        }
+    }
+
+    void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        canvas->scale(1.3f, 1.3f);
+        for (size_t i = 0; i < SK_ARRAY_COUNT(fTallBmps); ++i) {
+            SkASSERT(fTallBmps[i].fItemCnt > 10);
+            SkBitmap bmp = fTallBmps[i].fBmp;
+            // Draw the last 10 elements of the bitmap.
+            int startItem = fTallBmps[i].fItemCnt - 10;
+            int itemHeight = bmp.height() / fTallBmps[i].fItemCnt;
+            SkIRect subRect = SkIRect::MakeLTRB(0, startItem * itemHeight,
+                                               bmp.width(), bmp.height());
+            SkRect dstRect = SkRect::MakeWH(SkIntToScalar(bmp.width()), 10.f * itemHeight);
+            SkPaint paint;
+            paint.setFilterLevel(SkPaint::kLow_FilterLevel);
+            canvas->drawBitmapRect(bmp, &subRect, dstRect, &paint);
+            canvas->translate(SkIntToScalar(bmp.width() + 10), 0);
+        }
+    }    
+
+    uint32_t onGetFlags() const SK_OVERRIDE {
+        // This GM causes issues in replay modes.
+        return kSkipTiled_Flag | kNoBBH_Flag | kSkipPicture_Flag;
+    }
+
+private:
+    struct {
+        SkBitmap fBmp;
+        int      fItemCnt;
+    } fTallBmps[8];
+    typedef skiagm::GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM(return SkNEW(TallStretchedBitmapsGM);)
+