Fixed a bug with linear gradient PDF matrices and added test cases

gm/gradient_matrix.cpp

Index: gm/gradient_matrix.cpp
diff --git a/gm/gradient_matrix.cpp b/gm/gradient_matrix.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..cc1683e08939a197b9c0f246031faba68c8d700d
--- /dev/null
+++ b/gm/gradient_matrix.cpp
@@ -0,0 +1,111 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCanvas.h"
+#include "SkColor.h"
+#include "SkGradientShader.h"
+#include "SkMatrix.h"
+#include "SkPaint.h"
+#include "SkPoint.h"
+#include "SkRect.h"
+#include "SkRefCnt.h"
+#include "SkScalar.h"
+#include "SkSize.h"
+#include "SkString.h"
+
+#include "gm.h"
+
+static const SkColor gColors[] = {
+    SK_ColorRED, SK_ColorYELLOW
+};
+
+// these arrays define the gradient stop points
+// as x1, y1, x2, y2 per gradient to draw
+static const SkPoint linearPts[][2] = {
+    {{0, 0}, {1, 0}},
+    {{0, 0}, {0, 1}},
+    {{1, 0}, {0, 0}},
+    {{0, 1}, {0, 0}},
+
+    {{0, 0}, {1, 1}},
+    {{1, 1}, {0, 0}},
+    {{1, 0}, {0, 1}},
+    {{0, 1}, {1, 0}}
+};
+
+static const SkScalar TESTGRID_X = 200;    // pixels allocated to each image in x dimension
+static const SkScalar TESTGRID_Y = 200;    // pixels allocated to each image in y dimension
+
+static const int IMAGES_X = 4;             // number of images per row
+
+static SkShader* make_linear_gradient(const SkPoint pts[2]) {
+    return SkGradientShader::CreateLinear(pts, gColors, NULL, SK_ARRAY_COUNT(gColors),
+                                          SkShader::kClamp_TileMode, NULL);
+}
+
+static void draw_gradients(SkCanvas* canvas, SkShader* (*makeShader)(const SkPoint[2]),
+                    const SkPoint ptsArray[][2], int numImages) {
+    // Use some nice prime numbers for the rectangle and matrix with
+    // different scaling along the x and y axes (which is the bug this
+    // test addresses, where incorrect order of operations mixed up the axes)
+    SkRect rectGrad = { 43, 61, 181, 167 };
+    SkMatrix shaderMat;
+    shaderMat.setScale(rectGrad.width(), rectGrad.height());
+    shaderMat.postTranslate(rectGrad.left(), rectGrad.top());
+
+    canvas->save();
+    for (int i = 0; i < numImages; i++) {
+        // Advance line downwards if necessary.
+        if (i % IMAGES_X == 0 && i != 0) {
+            canvas->restore();
+            canvas->translate(0, TESTGRID_Y);
+            canvas->save();
+        }
+
+        // Setup shader and draw.
+        SkAutoTUnref<SkShader> shader(makeShader(*ptsArray));
+        shader->setLocalMatrix(shaderMat);
+
+        SkPaint paint;
+        paint.setShader(shader);
+        canvas->drawRect(rectGrad, paint);
+
+        // Advance to next position.
+        canvas->translate(TESTGRID_X, 0);
+        ptsArray++;
+    }
+    canvas->restore();
+}
+
+namespace skiagm {
+
+class GradientMatrixGM : public GM {
+public:
+    GradientMatrixGM() {
+        this->setBGColor(0xFFDDDDDD);
+    }
+
+protected:
+    SkString onShortName() SK_OVERRIDE {
+        return SkString("gradient_matrix");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return SkISize::Make(800, 800);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        draw_gradients(canvas, &make_linear_gradient,
+                      linearPts, SK_ARRAY_COUNT(linearPts));
+    }
+
+private:
+    typedef GM INHERITED;
+};
+
+DEF_GM( return new GradientMatrixGM; )
+}