Skip the transparent pixels when doing the sourceOver

Blending fully transparent pixels take a non-negligible time
when webkit use transparent layer. We can avoid that be skipping
those pixels since they have no impact on the final result.

Reviewed-by: Samuel Rødal

1 files changed, 6 insertions, 1 deletions

diff --git a/src/gui/painting/qdrawhelper_mmx_p.h b/src/gui/painting/qdrawhelper_mmx_p.h
index f8bc480..59b3804 100644
--- a/src/gui/painting/qdrawhelper_mmx_p.h
+++ b/src/gui/painting/qdrawhelper_mmx_p.h
@@ -240,7 +240,10 @@ static void QT_FASTCALL comp_func_SourceOver(uint *dest, const uint *src, int le
     C_FF; C_80; C_00;
     if (const_alpha == 255) {
         for (int i = 0; i < length; ++i) {
-            if ((0xff000000 & src[i]) == 0xff000000) {
+            const uint alphaMaskedSource = 0xff000000 & src[i];
+            if (alphaMaskedSource == 0)
+                continue;
+            if (alphaMaskedSource == 0xff000000) {
                 dest[i] = src[i];
             } else {
                 m64 s = MM::load(src[i]);
@@ -251,6 +254,8 @@ static void QT_FASTCALL comp_func_SourceOver(uint *dest, const uint *src, int le
     } else {
         m64 ca = MM::load_alpha(const_alpha);
         for (int i = 0; i < length; ++i) {
+            if ((0xff000000 & src[i]) == 0)
+                continue;
             m64 s = MM::byte_mul(MM::load(src[i]), ca);
             m64 ia = MM::negate(MM::alpha(s));
             dest[i] = MM::store(MM::add(s, MM::byte_mul(MM::load(dest[i]), ia)));