WebGL 2: add types into glReadPixels

Source/modules/webgl/WebGLRenderingContextBase.cpp

Index: Source/modules/webgl/WebGLRenderingContextBase.cpp
diff --git a/Source/modules/webgl/WebGLRenderingContextBase.cpp b/Source/modules/webgl/WebGLRenderingContextBase.cpp
index c18ea0b24ac9d1e3afc0d584c14def2d679e99a1..5885572583729d7bfbd17809612760ab69b44e66 100644
--- a/Source/modules/webgl/WebGLRenderingContextBase.cpp
+++ b/Source/modules/webgl/WebGLRenderingContextBase.cpp
@@ -3738,11 +3738,15 @@ void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsi
     case GL_BYTE:
         expectedViewType = DOMArrayBufferView::TypeInt8;
         break;
+    case GL_UNSIGNED_SHORT:

[Zhenyao Mo, 2015/08/13 15:22:01]

This is incorrect.  For OpenGL ES 2 / WebGL 1, it is clearly defined in Table
3.2 (page 62) what types are allowed.

[yunchao, 2015/08/14 00:07:11]

Yeah. I know that WebGL 1.0 should not support UNSIGNED_SHORT / SHORT. But for
these two types (and UNSIGNED_INT, UNSIGNED_INT_*, INT), the validation function
(validateReadPixelsFormatAndType) will report INVLID_ENUM and return. So the
code snippet is not wrong. 

Well, we  can override this code snippet respectively for WebGL 1 and WebGL 2 to
get 'expectedViewType', which should be more clearer. WDYT? 

     case GL_UNSIGNED_SHORT_5_6_5:
     case GL_UNSIGNED_SHORT_4_4_4_4:
     case GL_UNSIGNED_SHORT_5_5_5_1:
         expectedViewType = DOMArrayBufferView::TypeUint16;
         break;
+    case GL_SHORT:
+        expectedViewType = DOMArrayBufferView::TypeInt16;
+        break;
     case GL_FLOAT:
         expectedViewType = DOMArrayBufferView::TypeFloat32;
         break;