SkPDF: fix repeat tilemode with alpha

Also fix the corners of clamp mode with alpha.

Also, add a GM.

Bug:chromium:957275

Change-Id: Icd288ff522e7ea70662380791f5ee2de628a5ef2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/211594
Auto-Submit: Hal Canary <halcanary@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>

gm/tilemodes_alpha.cpp

@@ -0,0 +1,27 @@
+// Copyright 2019 Google LLC.
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+#include "gm/gm.h"
+#include "tools/Resources.h"
+// http://crbug.com/957275
+DEF_SIMPLE_GM(tilemodes_alpha, canvas, 512, 512) {
+    sk_sp<SkImage> image = GetResourceAsImage("images/mandrill_64.png");
+    if (!image) {
+        return;
+    }
+    constexpr SkTileMode kModes[4] = {
+        SkTileMode::kClamp,
+        SkTileMode::kRepeat,
+        SkTileMode::kMirror,
+        SkTileMode::kDecal,
+    };
+    for (int y = 0; y < 4; ++y) {
+        for (int x = 0; x < 4; ++x) {
+            SkRect rect = SkRect::MakeXYWH(128 * x + 1, 128 * y + 1, 126, 126);
+            SkMatrix matrix = SkMatrix::MakeTrans(rect.x(), rect.y());
+            SkPaint paint;
+            paint.setAlphaf(0.5f);
+            paint.setShader(image->makeShader(kModes[x], kModes[y], &matrix));
+            canvas->drawRect(rect, paint);
+        }
+    }
+}

gn/gm.gni

@@ -351,6 +351,7 @@ gm_sources = [
   "$_gm/tiledscaledbitmap.cpp",
   "$_gm/tileimagefilter.cpp",
   "$_gm/tilemodes.cpp",
+  "$_gm/tilemodes_alpha.cpp",
   "$_gm/tilemodes_scaled.cpp",
   "$_gm/tinybitmap.cpp",
   "$_gm/transparency.cpp",

src/pdf/SkPDFShader.cpp

@@ -9,6 +9,7 @@
 #include "src/pdf/SkPDFShader.h"
 
 #include "include/core/SkData.h"
+#include "include/core/SkMath.h"
 #include "include/core/SkScalar.h"
 #include "include/core/SkStream.h"
 #include "include/core/SkSurface.h"
@@ -37,6 +38,13 @@ static void draw_bitmap_matrix(SkCanvas* canvas, const SkBitmap& bm,
     canvas->drawBitmap(bm, 0, 0, &paint);
 }
 
+SkColor mix(SkColor c, U8CPU alpha) {
+    return SkColorSetARGB(SkMulDiv255Round(alpha, SkColorGetA(c)),
+                          SkColorGetR(c),
+                          SkColorGetG(c),
+                          SkColorGetB(c));
+}
+
 static SkPDFIndirectReference make_image_shader(SkPDFDocument* doc,
                                                 const SkPDFImageShaderKey& key,
                                                 SkImage* image) {
@@ -81,16 +89,17 @@ static SkPDFIndirectReference make_image_shader(SkPDFDocument* doc,
     // Undo the translation in the final matrix
     finalMatrix.preTranslate(deviceBounds.left(), deviceBounds.top());
 
+    SkPaint paint;
+    paint.setColor(key.fPaintColor);
+
     // If the bitmap is out of bounds (i.e. clamp mode where we only see the
     // stretched sides), canvas will clip this out and the extraneous data
     // won't be saved to the PDF.
-    canvas.drawImage(image, 0, 0);
+    canvas.drawImage(image, 0, 0, &paint);
 
     SkScalar width = SkIntToScalar(image->width());
     SkScalar height = SkIntToScalar(image->height());
 
-    SkPaint paint;
-    paint.setColor(key.fPaintColor);
     // Tiling is implied.  First we handle mirroring.
     if (tileModes[0] == SkTileMode::kMirror) {
         SkMatrix xMirror;
@@ -130,34 +139,35 @@ static SkPDFIndirectReference make_image_shader(SkPDFDocument* doc,
     // (Which are just a rectangles of the corner colors.)
     if (tileModes[0] == SkTileMode::kClamp && tileModes[1] == SkTileMode::kClamp) {
         SkASSERT(!bitmap.drawsNothing());
-        SkPaint paint;
+        U8CPU alpha = SkColorGetA(key.fPaintColor);
+        SkPaint paint2;
         SkRect rect;
         rect = SkRect::MakeLTRB(deviceBounds.left(), deviceBounds.top(), 0, 0);
         if (!rect.isEmpty()) {
-            paint.setColor(bitmap.getColor(0, 0));
-            canvas.drawRect(rect, paint);
+            paint2.setColor(mix(bitmap.getColor(0, 0), alpha));
+            canvas.drawRect(rect, paint2);
         }
 
         rect = SkRect::MakeLTRB(width, deviceBounds.top(),
                                 deviceBounds.right(), 0);
         if (!rect.isEmpty()) {
-            paint.setColor(bitmap.getColor(bitmap.width() - 1, 0));
-            canvas.drawRect(rect, paint);
+            paint2.setColor(mix(bitmap.getColor(bitmap.width() - 1, 0), alpha));
+            canvas.drawRect(rect, paint2);
         }
 
         rect = SkRect::MakeLTRB(width, height,
                                 deviceBounds.right(), deviceBounds.bottom());
         if (!rect.isEmpty()) {
-            paint.setColor(bitmap.getColor(bitmap.width() - 1,
-                                           bitmap.height() - 1));
-            canvas.drawRect(rect, paint);
+            paint2.setColor(mix(bitmap.getColor(bitmap.width() - 1,
+                                                bitmap.height() - 1), alpha));
+            canvas.drawRect(rect, paint2);
         }
 
         rect = SkRect::MakeLTRB(deviceBounds.left(), height,
                                 0, deviceBounds.bottom());
         if (!rect.isEmpty()) {
-            paint.setColor(bitmap.getColor(0, bitmap.height() - 1));
-            canvas.drawRect(rect, paint);
+            paint2.setColor(mix(bitmap.getColor(0, bitmap.height() - 1), alpha));
+            canvas.drawRect(rect, paint2);
         }
     }