X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=padding_effect.cpp;h=f7f97078e608749ab1a70db4226e2984be6281fb;hb=37f56fcbe571b2322243f6de59494bf9e0cbb37a;hp=c06a1ac49ef03b36cfa5ad338c71205aeb80d0b8;hpb=2322070a3dbeb6b46b39cca07a0fbf20e95f5468;p=movit

diff --git a/padding_effect.cpp b/padding_effect.cpp
index c06a1ac..f7f9707 100644
--- a/padding_effect.cpp
+++ b/padding_effect.cpp
@@ -1,5 +1,5 @@
-#include <math.h>
 #include <GL/glew.h>
+#include <assert.h>
 
 #include "padding_effect.h"
 #include "util.h"
@@ -89,14 +89,26 @@ bool PaddingEffect::needs_srgb_primaries() const
 	return true;
 }
 
-// If the border color is black, it doesn't matter if we're pre- or postmultiplied
-// (or even blank, as a hack). Otherwise, it does.
 Effect::AlphaHandling PaddingEffect::alpha_handling() const
 {
-	if (border_color.r == 0.0 && border_color.g == 0.0 && border_color.b == 0.0) {
+	// If the border color is black, it doesn't matter if we're pre- or postmultiplied.
+	// Note that for non-solid black (i.e. alpha < 1.0), we're equally fine with
+	// pre- and postmultiplied, but later effects might change this status
+	// (consider e.g. blur), so setting DONT_CARE_ALPHA_TYPE is inappropriate,
+	// as it propagate blank alpha through this effect.
+	if (border_color.r == 0.0 && border_color.g == 0.0 && border_color.b == 0.0 && border_color.a == 1.0) {
 		return DONT_CARE_ALPHA_TYPE;
 	}
-	return INPUT_AND_OUTPUT_ALPHA_PREMULTIPLIED;
+
+	// If the border color is solid, we preserve blank alpha, as we never output any
+	// new non-solid pixels.
+	if (border_color.a == 1.0) {
+		return INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK;
+	}
+
+	// Otherwise, we're going to output our border color in premultiplied alpha,
+	// so the other pixels better be premultiplied as well.
+	return INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA;
 }
 	
 void PaddingEffect::get_output_size(unsigned *width, unsigned *height, unsigned *virtual_width, unsigned *virtual_height) const