-#include <math.h>
#include <GL/glew.h>
+#include <assert.h>
+#include "effect_util.h"
#include "padding_effect.h"
#include "util.h"
// 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;
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;
}