Fix subpixel rendered text in QGLWidget

Subpixel rendered text doesn't work in the old OpenGL paint engine
because it assumes the glyphs are returned in RGB32 format, when they
may be in ARGB32. This patch changes the test of the returned format
to just check for 32bit matching the logic in the new OpenGL paint
engine.

Change-Id: Ib5b784dedba51cf22f216e2f035361518610b96b
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>

src/opengl/gl2paintengineex/qtextureglyphcache_gl.cpp

@@ -304,19 +304,23 @@ void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph, QFixed sub
             for (int x = 0; x < maskWidth; ++x)
                 src[x] = -src[x]; // convert 0 and 1 into 0 and 255
         }
-    } else if (mask.format() == QImage::Format_RGB32) {
+    } else if (mask.depth() == 32) {
         // Make the alpha component equal to the average of the RGB values.
         // This is needed when drawing sub-pixel antialiased text on translucent targets.
         for (int y = 0; y < maskHeight; ++y) {
             quint32 *src = (quint32 *) mask.scanLine(y);
             for (int x = 0; x < maskWidth; ++x) {
-                uchar r = src[x] >> 16;
-                uchar g = src[x] >> 8;
-                uchar b = src[x];
-                quint32 avg = (quint32(r) + quint32(g) + quint32(b) + 1) / 3; // "+1" for rounding.
+                int r = qRed(src[x]);
+                int g = qGreen(src[x]);
+                int b = qBlue(src[x]);
+                int avg;
+                if (mask.format() == QImage::Format_RGB32)
+                    avg = (r + g + b + 1) / 3; // "+1" for rounding.
+                else // Format_ARGB_Premultiplied
+                    avg = qAlpha(src[x]);
                 if (ctx->contextHandle()->isOpenGLES()) {
                     // swizzle the bits to accommodate for the GL_RGBA upload.
-                    src[x] = (avg << 24) | (quint32(r) << 0) | (quint32(g) << 8) | (quint32(b) << 16);
+                    src[x] = (avg << 24) | (r << 0) | (g << 8) | (b << 16);
                 } else {
                     src[x] = (src[x] & 0x00ffffff) | (avg << 24);
                 }
@@ -325,7 +329,7 @@ void QGLTextureGlyphCache::fillTexture(const Coord &c, glyph_t glyph, QFixed sub
     }
 
     funcs->glBindTexture(GL_TEXTURE_2D, m_textureResource->m_texture);
-    if (mask.format() == QImage::Format_RGB32) {
+    if (mask.depth() == 32) {
         GLenum format = GL_RGBA;
 #if !defined(QT_OPENGL_ES_2)
         if (!ctx->contextHandle()->isOpenGLES())