Add a new alpha handling method, INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK.

[movit] / effect_chain.cpp

diff --git a/effect_chain.cpp b/effect_chain.cpp
index bd039b0113e662a9279976a3d01ed43e2a406102..0f8876d8f70c68ccb6b4d2a41a538414eddf9efe 100644 (file)
--- a/effect_chain.cpp
+++ b/effect_chain.cpp
@@ -782,6 +782,7 @@ void EffectChain::find_color_spaces_for_inputs()
                        case Effect::OUTPUT_POSTMULTIPLIED_ALPHA:
                                node->output_alpha_type = ALPHA_POSTMULTIPLIED;
                                break;
+                       case Effect::INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK:
                        case Effect::DONT_CARE_ALPHA_TYPE:
                        default:
                                assert(false);
@@ -894,6 +895,7 @@ void EffectChain::propagate_alpha()
                // whether to divide away the old alpha or not.
                Effect::AlphaHandling alpha_handling = node->effect->alpha_handling();
                assert(alpha_handling == Effect::INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA ||
+                      alpha_handling == Effect::INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK ||
                       alpha_handling == Effect::DONT_CARE_ALPHA_TYPE);
 
                // If the node has multiple inputs, check that they are all valid and
@@ -933,16 +935,16 @@ void EffectChain::propagate_alpha()
                        continue;
                }
 
-               if (alpha_handling == Effect::INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA) {
+               if (alpha_handling == Effect::INPUT_AND_OUTPUT_PREMULTIPLIED_ALPHA ||
+                   alpha_handling == Effect::INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK) {
                        // If the effect has asked for premultiplied alpha, check that it has got it.
                        if (any_postmultiplied) {
                                node->output_alpha_type = ALPHA_INVALID;
+                       } else if (!any_premultiplied &&
+                                  alpha_handling == Effect::INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK) {
+                               // Blank input alpha, and the effect preserves blank alpha.
+                               node->output_alpha_type = ALPHA_BLANK;
                        } else {
-                               // In some rare cases, it might be advantageous to say
-                               // that blank input alpha yields blank output alpha.
-                               // However, this would cause a more complex Effect interface
-                               // an effect would need to guarantee that it doesn't mess with
-                               // blank alpha), so this is the simplest.
                                node->output_alpha_type = ALPHA_PREMULTIPLIED;
                        }
                } else {