nodes: allow two texture inputs in opacity

app/node/effect/opacity/opacityeffect.cpp

@@ -39,15 +39,22 @@ void OpacityEffect::Retranslate()
 
 ShaderCode OpacityEffect::GetShaderCode(const ShaderRequest &request) const
 {
-  Q_UNUSED(request)
-  return ShaderCode(FileFunctions::ReadFileAsString(":/shaders/opacity.frag"));
+  if (request.id == QStringLiteral("rgbmult")) {
+    return ShaderCode(FileFunctions::ReadFileAsString(":/shaders/opacity_rgb.frag"));
+  } else {
+    return ShaderCode(FileFunctions::ReadFileAsString(":/shaders/opacity.frag"));
+  }
 }
 
 void OpacityEffect::Value(const NodeValueRow &value, const NodeGlobals &globals, NodeValueTable *table) const
 {
   // If there's no texture, no need to run an operation
   if (TexturePtr tex = value[kTextureInput].toTexture()) {
-    if (!qFuzzyCompare(value[kValueInput].toDouble(), 1.0)) {
+    if (TexturePtr opacity_tex = value[kValueInput].toTexture()) {
+      ShaderJob job(value);
+      job.SetShaderID(QStringLiteral("rgbmult"));
+      table->Push(NodeValue::kTexture, tex->toJob(job), this);
+    } else if (!qFuzzyCompare(value[kValueInput].toDouble(), 1.0)) {
       table->Push(NodeValue::kTexture, tex->toJob(ShaderJob(value)), this);
     } else {
       // 1.0 float is a no-op, so just push the texture

app/shaders/opacity_rgb.frag

@@ -0,0 +1,27 @@
+// Inputs
+uniform sampler2D tex_in;
+uniform sampler2D opacity_in;
+
+// Input texture coordinate
+in vec2 ove_texcoord;
+out vec4 frag_color;
+
+vec3 rgb2hsv(vec3 c)
+{
+  vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
+  vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
+  vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));
+
+  float d = q.x - min(q.w, q.y);
+  float e = 1.0e-10;
+  return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
+}
+
+void main() {
+  vec4 value = texture(opacity_in, ove_texcoord);
+  float v = rgb2hsv(value.rgb).b;
+
+  vec4 c = texture(tex_in, ove_texcoord);
+  c *= v;
+  frag_color = c;
+}