X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=padding_effect.cpp;h=00d475ac2fb23995780920569ee09203abb91177;hp=3c4919a0c3b1b98a3aa31ebf9aad14ff536bcdcf;hb=5c97329dd35909847e2120b0b368b2723ffe5a44;hpb=5d4c0425579de66b3e2dd7d0095e890278f8efcf;ds=sidebyside

diff --git a/padding_effect.cpp b/padding_effect.cpp
index 3c4919a..00d475a 100644
--- a/padding_effect.cpp
+++ b/padding_effect.cpp
@@ -1,6 +1,7 @@
-#include <math.h>
 #include <GL/glew.h>
+#include <assert.h>
 
+#include "effect_util.h"
 #include "padding_effect.h"
 #include "util.h"
 
@@ -63,12 +64,16 @@ void PaddingEffect::set_gl_state(GLuint glsl_program_num, const std::string &pre
 // differently in different modes.
 
 // 0.0 and 1.0 are interpreted the same, no matter the gamma ramp.
-// Alpha is not affected by gamma.
+// Alpha is not affected by gamma per se, but the combination of
+// premultiplied alpha and non-linear gamma curve does not make sense,
+// so if could possibly be converting blank alpha to non-blank
+// (ie., premultiplied), we need our output to be in linear light.
 bool PaddingEffect::needs_linear_light() const
 {
 	if ((border_color.r == 0.0 || border_color.r == 1.0) &&
 	    (border_color.g == 0.0 || border_color.g == 1.0) &&
-	    (border_color.b == 0.0 || border_color.b == 1.0)) {
+	    (border_color.b == 0.0 || border_color.b == 1.0) &&
+	    border_color.a == 1.0) {
 		return false;
 	}
 	return true;
@@ -89,13 +94,25 @@ 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;
 	}
+
+	// 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;
 }