Support tiling bitmaps outside clip bounds in SkPDFImageShader

src/pdf/SkPDFShader.cpp

Index: src/pdf/SkPDFShader.cpp
diff --git a/src/pdf/SkPDFShader.cpp b/src/pdf/SkPDFShader.cpp
index 9394f1b9597c67d25e77a99af74e2bf938fdd4c8..1d8792c1f13c3c8cf0366d054d2ce970699afdaf 100644
--- a/src/pdf/SkPDFShader.cpp
+++ b/src/pdf/SkPDFShader.cpp
@@ -24,7 +24,7 @@
 #include "SkTSet.h"
 #include "SkTypes.h"
 
-static bool transformBBox(const SkMatrix& matrix, SkRect* bbox) {
+static bool inverseTransformBBox(const SkMatrix& matrix, SkRect* bbox) {
     SkMatrix inverse;
     if (!matrix.invert(&inverse)) {
         return false;
@@ -780,7 +780,7 @@ SkPDFFunctionShader::SkPDFFunctionShader(SkPDFShader::State* state)
 
     SkRect bbox;
     bbox.set(fState.get()->fBBox);
-    if (!transformBBox(finalMatrix, &bbox)) {
+    if (!inverseTransformBBox(finalMatrix, &bbox)) {
         return;
     }
 
@@ -828,35 +828,55 @@ SkPDFFunctionShader::SkPDFFunctionShader(SkPDFShader::State* state)
 SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
     fState.get()->fImage.lockPixels();
 
+    // The image shader pattern cell will be drawn into a separate device
+    // in pattern cell space (no scaling on the bitmap, though there may be
+    // translations so that all content is in the device, coordinates > 0).
+
+    // Map clip bounds to shader space to ensure the device is large enough
+    // to handle fake clamping.
     SkMatrix finalMatrix = fState.get()->fCanvasTransform;
     finalMatrix.preConcat(fState.get()->fShaderTransform);
-    SkRect surfaceBBox;
-    surfaceBBox.set(fState.get()->fBBox);
-    if (!transformBBox(finalMatrix, &surfaceBBox)) {
+    SkRect deviceBounds;
+    deviceBounds.set(fState.get()->fBBox);
+    if (!inverseTransformBBox(finalMatrix, &deviceBounds)) {
         return;
     }
 
+    // Ensure the device bounds include the pattern cell as tiling theoretically
+    // extends out to infinity. If the device size is too small, the pattern
+    // cell bitmap will be clipped out, and the shader will look awful.
+    const SkBitmap* image = &fState.get()->fImage;

[vandebo (ex-Chrome), 2013/08/20 17:22:19]

I think you don't want to do this for clamp mode.  In clamp mode, not drawing
the things that will get clipped is the right thing to do.

[ducky, 2013/08/21 00:44:08]

Done.

+    SkRect bitmapBounds;
+    image->getBounds(&bitmapBounds);
+    deviceBounds.join(bitmapBounds);
+
     SkMatrix unflip;
-    unflip.setTranslate(0, SkScalarRoundToScalar(surfaceBBox.height()));
+    unflip.setTranslate(0, SkScalarRoundToScalar(deviceBounds.height()));
     unflip.preScale(SK_Scalar1, -SK_Scalar1);
-    SkISize size = SkISize::Make(SkScalarRound(surfaceBBox.width()),
-                                 SkScalarRound(surfaceBBox.height()));
+    SkISize size = SkISize::Make(SkScalarRound(deviceBounds.width()),
+                                 SkScalarRound(deviceBounds.height()));
     SkPDFDevice pattern(size, size, unflip);
     SkCanvas canvas(&pattern);
-    canvas.translate(-surfaceBBox.fLeft, -surfaceBBox.fTop);
-    finalMatrix.preTranslate(surfaceBBox.fLeft, surfaceBBox.fTop);
 
-    const SkBitmap* image = &fState.get()->fImage;
-    SkScalar width = SkIntToScalar(image->width());
-    SkScalar height = SkIntToScalar(image->height());
+    SkRect patternBBox;
+    image->getBounds(&patternBBox);
+    // Translate canvas origin to bitmap origin so all coordinates are > 0
+    // (inside device clip bounds).
+    if (deviceBounds.left() < 0 || deviceBounds.top() < 0) {

[vandebo (ex-Chrome), 2013/08/20 17:22:19]

Why do this conditionally?  What if the pattern is located off the right side or
the bottom of the canvas?

[ducky, 2013/08/21 00:44:08]

The bitmap origin is at (0, 0), so the joined rectangle (if the clip bounds are
at the right / bottom side) should be anchored to (0, 0).

Though with clamp mode no longer including the bitmap, the conditional has been
removed.

+        canvas.translate(-deviceBounds.left(), -deviceBounds.top());
+        patternBBox.offset(-deviceBounds.left(), -deviceBounds.top());
+        // Undo the translation in the final matrix
+        finalMatrix.preTranslate(deviceBounds.left(), deviceBounds.top());
+    }
+
+    canvas.drawBitmap(*image, 0, 0);
+
+    SkScalar width = image->width();
+    SkScalar height = image->height();
     SkShader::TileMode tileModes[2];
     tileModes[0] = fState.get()->fImageTileModes[0];
     tileModes[1] = fState.get()->fImageTileModes[1];
 
-    canvas.drawBitmap(*image, 0, 0);
-    SkRect patternBBox = SkRect::MakeXYWH(-surfaceBBox.fLeft, -surfaceBBox.fTop,
-                                          width, height);
-
     // Tiling is implied.  First we handle mirroring.
     if (tileModes[0] == SkShader::kMirror_TileMode) {
         SkMatrix xMirror;
@@ -889,28 +909,29 @@ SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
             tileModes[1] == SkShader::kClamp_TileMode) {
         SkPaint paint;
         SkRect rect;
-        rect = SkRect::MakeLTRB(surfaceBBox.fLeft, surfaceBBox.fTop, 0, 0);
+        rect = SkRect::MakeLTRB(deviceBounds.left(), deviceBounds.top(), 0, 0);
         if (!rect.isEmpty()) {
             paint.setColor(image->getColor(0, 0));
             canvas.drawRect(rect, paint);
         }
 
-        rect = SkRect::MakeLTRB(width, surfaceBBox.fTop, surfaceBBox.fRight, 0);
+        rect = SkRect::MakeLTRB(width, deviceBounds.top(),
+                                deviceBounds.right(), 0);
         if (!rect.isEmpty()) {
             paint.setColor(image->getColor(image->width() - 1, 0));
             canvas.drawRect(rect, paint);
         }
 
-        rect = SkRect::MakeLTRB(width, height, surfaceBBox.fRight,
-                                surfaceBBox.fBottom);
+        rect = SkRect::MakeLTRB(width, height,
+                                deviceBounds.right(), deviceBounds.bottom());
         if (!rect.isEmpty()) {
             paint.setColor(image->getColor(image->width() - 1,
                                            image->height() - 1));
             canvas.drawRect(rect, paint);
         }
 
-        rect = SkRect::MakeLTRB(surfaceBBox.fLeft, height, 0,
-                                surfaceBBox.fBottom);
+        rect = SkRect::MakeLTRB(deviceBounds.left(), height,
+                                0, deviceBounds.bottom());
         if (!rect.isEmpty()) {
             paint.setColor(image->getColor(0, image->height() - 1));
             canvas.drawRect(rect, paint);
@@ -920,13 +941,13 @@ SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
     // Then expand the left, right, top, then bottom.
     if (tileModes[0] == SkShader::kClamp_TileMode) {
         SkIRect subset = SkIRect::MakeXYWH(0, 0, 1, image->height());
-        if (surfaceBBox.fLeft < 0) {
+        if (deviceBounds.left() < 0) {
             SkBitmap left;
             SkAssertResult(image->extractSubset(&left, subset));
 
             SkMatrix leftMatrix;
-            leftMatrix.setScale(-surfaceBBox.fLeft, 1);
-            leftMatrix.postTranslate(surfaceBBox.fLeft, 0);
+            leftMatrix.setScale(-deviceBounds.left(), 1);
+            leftMatrix.postTranslate(deviceBounds.left(), 0);
             canvas.drawBitmapMatrix(left, leftMatrix);
 
             if (tileModes[1] == SkShader::kMirror_TileMode) {
@@ -937,13 +958,13 @@ SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
             patternBBox.fLeft = 0;
         }
 
-        if (surfaceBBox.fRight > width) {
+        if (deviceBounds.right() > width) {
             SkBitmap right;
             subset.offset(image->width() - 1, 0);
             SkAssertResult(image->extractSubset(&right, subset));
 
             SkMatrix rightMatrix;
-            rightMatrix.setScale(surfaceBBox.fRight - width, 1);
+            rightMatrix.setScale(deviceBounds.right() - width, 1);
             rightMatrix.postTranslate(width, 0);
             canvas.drawBitmapMatrix(right, rightMatrix);
 
@@ -952,19 +973,19 @@ SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
                 rightMatrix.postTranslate(0, 2 * height);
                 canvas.drawBitmapMatrix(right, rightMatrix);
             }
-            patternBBox.fRight = surfaceBBox.width();
+            patternBBox.fRight = deviceBounds.width();
         }
     }
 
     if (tileModes[1] == SkShader::kClamp_TileMode) {
         SkIRect subset = SkIRect::MakeXYWH(0, 0, image->width(), 1);
-        if (surfaceBBox.fTop < 0) {
+        if (deviceBounds.top() < 0) {
             SkBitmap top;
             SkAssertResult(image->extractSubset(&top, subset));
 
             SkMatrix topMatrix;
-            topMatrix.setScale(SK_Scalar1, -surfaceBBox.fTop);
-            topMatrix.postTranslate(0, surfaceBBox.fTop);
+            topMatrix.setScale(SK_Scalar1, -deviceBounds.top());
+            topMatrix.postTranslate(0, deviceBounds.top());
             canvas.drawBitmapMatrix(top, topMatrix);
 
             if (tileModes[0] == SkShader::kMirror_TileMode) {
@@ -975,13 +996,13 @@ SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
             patternBBox.fTop = 0;
         }
 
-        if (surfaceBBox.fBottom > height) {
+        if (deviceBounds.bottom() > height) {
             SkBitmap bottom;
             subset.offset(0, image->height() - 1);
             SkAssertResult(image->extractSubset(&bottom, subset));
 
             SkMatrix bottomMatrix;
-            bottomMatrix.setScale(SK_Scalar1, surfaceBBox.fBottom - height);
+            bottomMatrix.setScale(SK_Scalar1, deviceBounds.bottom() - height);
             bottomMatrix.postTranslate(0, height);
             canvas.drawBitmapMatrix(bottom, bottomMatrix);
 
@@ -990,7 +1011,7 @@ SkPDFImageShader::SkPDFImageShader(SkPDFShader::State* state) : fState(state) {
                 bottomMatrix.postTranslate(2 * width, 0);
                 canvas.drawBitmapMatrix(bottom, bottomMatrix);
             }
-            patternBBox.fBottom = surfaceBBox.height();
+            patternBBox.fBottom = deviceBounds.height();
         }
     }