Improve ImageData::StorageFormatDataSize

ImageData::StorageFormatDataSize returns 1, 2 and 4 for the data size
for color format in uint8, uint16 and float 32 format, respectively.
This not really true, since we need 4 channel to describe a color, the
data size should really be 4, 8 and 16 bytes instead. In image_data.cc,
we always call ImageData::StorageFormatDataSize and then multiply the
result by 4 to get the real data size.

In this cl, I update ImageData::StorageFormatDataSize to return 4, 8 and
16 and remove the multiplication to improve the readability of the code.

Bug: 1122866

Change-Id: Ib78e31cff3c919728a3a84771acf2545d29a89a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391984Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Reviewed-by: Juanmi Huertas <juanmihd@chromium.org>
Reviewed-by: Aaron Krajeski <aaronhk@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: Yi Xu <yiyix@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805976}

third_party/blink/renderer/bindings/core/v8/serialization/v8_script_value_deserializer.cc

@@ -425,8 +425,8 @@ ScriptWrappable* V8ScriptValueDeserializer::ReadDOMObject(
       ImageDataStorageFormat storage_format = color_params.GetStorageFormat();
       base::CheckedNumeric<size_t> computed_byte_length = width;
       computed_byte_length *= height;
-      computed_byte_length *= 4;
-      computed_byte_length *= ImageData::StorageFormatDataSize(storage_format);
+      computed_byte_length *=
+          ImageData::StorageFormatBytesPerPixel(storage_format);
       if (!computed_byte_length.IsValid() ||
           computed_byte_length.ValueOrDie() != byte_length)
         return nullptr;

third_party/blink/renderer/core/html/canvas/image_data.cc

@@ -78,10 +78,12 @@ bool ImageData::ValidateConstructorArguments(
   }
 
   if (param_flags & (kParamWidth | kParamHeight)) {
-    base::CheckedNumeric<unsigned> data_size = 4;
+    base::CheckedNumeric<unsigned> data_size =
+        ImageData::StorageFormatBytesPerPixel(
+            kUint8ClampedArrayStorageFormatName);
     if (color_settings) {
-      data_size *=
-          ImageData::StorageFormatDataSize(color_settings->storageFormat());
+      data_size = ImageData::StorageFormatBytesPerPixel(
+          color_settings->storageFormat());
     }
     data_size *= width;
     data_size *= height;
@@ -373,7 +375,10 @@ ImageData* ImageData::Create(unsigned width,
     return nullptr;
 
   NotShared<DOMUint8ClampedArray> byte_array =
-      AllocateAndValidateUint8ClampedArray(4 * width * height,
+      AllocateAndValidateUint8ClampedArray(
+          ImageData::StorageFormatBytesPerPixel(
+              kUint8ClampedArrayStorageFormat) *
+              width * height,
           &exception_state);
   return byte_array ? MakeGarbageCollected<ImageData>(IntSize(width, height),
                                                       byte_array)
@@ -467,7 +472,8 @@ ImageData* ImageData::CreateImageData(ImageDataArray& data,
 // This function accepts size (0, 0) and always returns the ImageData in
 // "srgb" color space and "uint8" storage format.
 ImageData* ImageData::CreateForTest(const IntSize& size) {
-  base::CheckedNumeric<unsigned> data_size = 4;
+  base::CheckedNumeric<unsigned> data_size =
+      ImageData::StorageFormatBytesPerPixel(kUint8ClampedArrayStorageFormat);
   data_size *= size.Width();
   data_size *= size.Height();
   if (!data_size.IsValid() ||
@@ -517,7 +523,7 @@ ImageData* ImageData::CropRect(const IntRect& crop_rect, bool flip_y) {
                 data_size * buffer_view->TypeSize());
   } else {
     unsigned data_type_size =
-        ImageData::StorageFormatDataSize(color_settings_->storageFormat());
+        ImageData::StorageFormatBytesPerPixel(color_settings_->storageFormat());
     int src_index = (dst_rect.X() + dst_rect.Y() * src_rect.Width()) * 4;
     int dst_index = 0;
     if (flip_y)
@@ -525,11 +531,11 @@ ImageData* ImageData::CropRect(const IntRect& crop_rect, bool flip_y) {
     int src_row_stride = src_rect.Width() * 4;
     int dst_row_stride = flip_y ? -dst_rect.Width() * 4 : dst_rect.Width() * 4;
     for (int i = 0; i < dst_rect.Height(); i++) {
-      std::memcpy(
-          static_cast<char*>(buffer_view->BufferBase()->Data()) +
-              dst_index * data_type_size,
-          static_cast<char*>(BufferBase()->Data()) + src_index * data_type_size,
-          dst_rect.Width() * 4 * data_type_size);
+      std::memcpy(static_cast<char*>(buffer_view->BufferBase()->Data()) +
+                      dst_index / 4 * data_type_size,
+                  static_cast<char*>(BufferBase()->Data()) +
+                      src_index / 4 * data_type_size,
+                  dst_rect.Width() * data_type_size);
       src_index += src_row_stride;
       dst_index += dst_row_stride;
     }
@@ -635,26 +641,27 @@ ImageDataStorageFormat ImageData::GetImageDataStorageFormat() {
   return kUint8ClampedArrayStorageFormat;
 }
 
-unsigned ImageData::StorageFormatDataSize(const String& storage_format_name) {
+unsigned ImageData::StorageFormatBytesPerPixel(
+    const String& storage_format_name) {
   if (storage_format_name == kUint8ClampedArrayStorageFormatName)
-    return 1;
+    return 4;
   if (storage_format_name == kUint16ArrayStorageFormatName)
-    return 2;
+    return 8;
   if (storage_format_name == kFloat32ArrayStorageFormatName)
-    return 4;
+    return 16;
   NOTREACHED();
   return 1;
 }
 
-unsigned ImageData::StorageFormatDataSize(
+unsigned ImageData::StorageFormatBytesPerPixel(
     ImageDataStorageFormat storage_format) {
   switch (storage_format) {
     case kUint8ClampedArrayStorageFormat:
-      return 1;
+      return 4;
     case kUint16ArrayStorageFormat:
-      return 2;
+      return 8;
     case kFloat32ArrayStorageFormat:
-      return 4;
+      return 16;
   }
   NOTREACHED();
   return 1;
@@ -802,7 +809,7 @@ bool ImageData::ImageDataInCanvasColorSettings(
   // for every line.
   if (crop_rect) {
     unsigned bytes_per_pixel =
-        ImageData::StorageFormatDataSize(storage_format) * 4;
+        ImageData::StorageFormatBytesPerPixel(storage_format);
     unsigned src_index =
         (crop_rect->X() + crop_rect->Y() * width()) * bytes_per_pixel;
     unsigned dst_index = 0;

third_party/blink/renderer/core/html/canvas/image_data.h

@@ -117,8 +117,8 @@ class CORE_EXPORT ImageData final : public ScriptWrappable,
   static CanvasColorSpace GetCanvasColorSpace(const String&);
   static String CanvasColorSpaceName(CanvasColorSpace);
   static ImageDataStorageFormat GetImageDataStorageFormat(const String&);
-  static unsigned StorageFormatDataSize(const String&);
-  static unsigned StorageFormatDataSize(ImageDataStorageFormat);
+  static unsigned StorageFormatBytesPerPixel(const String&);
+  static unsigned StorageFormatBytesPerPixel(ImageDataStorageFormat);
   static NotShared<DOMArrayBufferView>
   ConvertPixelsFromCanvasPixelFormatToImageDataStorageFormat(
       ArrayBufferContents&,