Adding composite/blend modes to libopenshot:

-Normal
-Darken
-Multiply
-Color Burn
-Lighten
-Screen
-Color Dodge
-Add
-Overlay
-Soft Light
-Hard Light
-Difference
-Exclusion

src/Clip.cpp

@@ -32,6 +32,34 @@
 
 using namespace openshot;
 
+namespace {
+	struct CompositeChoice { const char* name; CompositeType value; };
+	const CompositeChoice composite_choices[] = {
+		{"Normal",      COMPOSITE_SOURCE_OVER},
+
+		// Darken group
+		{"Darken",      COMPOSITE_DARKEN},
+		{"Multiply",    COMPOSITE_MULTIPLY},
+		{"Color Burn",  COMPOSITE_COLOR_BURN},
+
+		// Lighten group
+		{"Lighten",     COMPOSITE_LIGHTEN},
+		{"Screen",      COMPOSITE_SCREEN},
+		{"Color Dodge", COMPOSITE_COLOR_DODGE},
+		{"Add",         COMPOSITE_PLUS},
+
+		// Contrast group
+		{"Overlay",     COMPOSITE_OVERLAY},
+		{"Soft Light",  COMPOSITE_SOFT_LIGHT},
+		{"Hard Light",  COMPOSITE_HARD_LIGHT},
+
+		// Compare
+		{"Difference",  COMPOSITE_DIFFERENCE},
+		{"Exclusion",   COMPOSITE_EXCLUSION},
+	};
+	const int composite_choices_count = sizeof(composite_choices)/sizeof(CompositeChoice);
+}
+
 // Init default settings for a clip
 void Clip::init_settings()
 {
@@ -45,6 +73,7 @@ void Clip::init_settings()
 	anchor = ANCHOR_CANVAS;
 	display = FRAME_DISPLAY_NONE;
 	mixing = VOLUME_MIX_NONE;
+	composite = COMPOSITE_SOURCE_OVER;
 	waveform = false;
 	previous_properties = "";
 	parentObjectId = "";
@@ -766,6 +795,7 @@ std::string Clip::PropertiesJSON(int64_t requested_frame) const {
 	root["scale"] = add_property_json("Scale", scale, "int", "", NULL, 0, 3, false, requested_frame);
 	root["display"] = add_property_json("Frame Number", display, "int", "", NULL, 0, 3, false, requested_frame);
 	root["mixing"] = add_property_json("Volume Mixing", mixing, "int", "", NULL, 0, 2, false, requested_frame);
+	root["composite"] = add_property_json("Composite", composite, "int", "", NULL, 0, composite_choices_count - 1, false, requested_frame);
 	root["waveform"] = add_property_json("Waveform", waveform, "int", "", NULL, 0, 1, false, requested_frame);
 	root["parentObjectId"] = add_property_json("Parent", 0.0, "string", parentObjectId, NULL, -1, -1, false, requested_frame);
 
@@ -797,6 +827,10 @@ std::string Clip::PropertiesJSON(int64_t requested_frame) const {
 	root["mixing"]["choices"].append(add_property_choice_json("Average", VOLUME_MIX_AVERAGE, mixing));
 	root["mixing"]["choices"].append(add_property_choice_json("Reduce", VOLUME_MIX_REDUCE, mixing));
 
+	// Add composite choices (dropdown style)
+	for (int i = 0; i < composite_choices_count; ++i)
+		root["composite"]["choices"].append(add_property_choice_json(composite_choices[i].name, composite_choices[i].value, composite));
+
 	// Add waveform choices (dropdown style)
 	root["waveform"]["choices"].append(add_property_choice_json("Yes", true, waveform));
 	root["waveform"]["choices"].append(add_property_choice_json("No", false, waveform));
@@ -879,6 +913,7 @@ Json::Value Clip::JsonValue() const {
 	root["anchor"] = anchor;
 	root["display"] = display;
 	root["mixing"] = mixing;
+	root["composite"] = composite;
 	root["waveform"] = waveform;
 	root["scale_x"] = scale_x.JsonValue();
 	root["scale_y"] = scale_y.JsonValue();
@@ -967,6 +1002,8 @@ void Clip::SetJsonValue(const Json::Value root) {
 		display = (FrameDisplayType) root["display"].asInt();
 	if (!root["mixing"].isNull())
 		mixing = (VolumeMixType) root["mixing"].asInt();
+	if (!root["composite"].isNull())
+		composite = (CompositeType) root["composite"].asInt();
 	if (!root["waveform"].isNull())
 		waveform = root["waveform"].asBool();
 	if (!root["scale_x"].isNull())
@@ -1197,7 +1234,7 @@ void Clip::apply_background(std::shared_ptr<openshot::Frame> frame, std::shared_
 	QPainter painter(background_canvas.get());
 
 	// Composite a new layer onto the image
-	painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
+	painter.setCompositionMode(static_cast<QPainter::CompositionMode>(composite));
 	painter.drawImage(0, 0, *frame->GetImage());
 	painter.end();
 
@@ -1260,7 +1297,7 @@ void Clip::apply_keyframes(std::shared_ptr<Frame> frame, QSize timeline_size) {
 	painter.setTransform(transform);
 
 	// Composite a new layer onto the image
-	painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
+	painter.setCompositionMode(static_cast<QPainter::CompositionMode>(composite));
 
 	// Apply opacity via painter instead of per-pixel alpha manipulation
 	const float alpha_value = alpha.GetValue(frame->number);

src/Clip.h

@@ -169,6 +169,7 @@ namespace openshot {
 		openshot::AnchorType anchor;	 ///< The anchor determines what parent a clip should snap to
 		openshot::FrameDisplayType display; ///< The format to display the frame number (if any)
 		openshot::VolumeMixType mixing;  ///< What strategy should be followed when mixing audio with other clips
+		openshot::CompositeType composite; ///< How this clip is composited onto lower layers
 
 		#ifdef USE_OPENCV
 			bool COMPILED_WITH_CV = true;

src/Enums.h

@@ -64,6 +64,37 @@ enum VolumeMixType
 	VOLUME_MIX_REDUCE 	///< Reduce volume by about %25, and then mix (louder, but could cause pops if the sum exceeds 100%)
 };
 
+/// This enumeration determines how clips are composited onto lower layers.
+enum CompositeType {
+	COMPOSITE_SOURCE_OVER,
+	COMPOSITE_DESTINATION_OVER,
+	COMPOSITE_CLEAR,
+	COMPOSITE_SOURCE,
+	COMPOSITE_DESTINATION,
+	COMPOSITE_SOURCE_IN,
+	COMPOSITE_DESTINATION_IN,
+	COMPOSITE_SOURCE_OUT,
+	COMPOSITE_DESTINATION_OUT,
+	COMPOSITE_SOURCE_ATOP,
+	COMPOSITE_DESTINATION_ATOP,
+	COMPOSITE_XOR,
+
+	// svg 1.2 blend modes
+	COMPOSITE_PLUS,
+	COMPOSITE_MULTIPLY,
+	COMPOSITE_SCREEN,
+	COMPOSITE_OVERLAY,
+	COMPOSITE_DARKEN,
+	COMPOSITE_LIGHTEN,
+	COMPOSITE_COLOR_DODGE,
+	COMPOSITE_COLOR_BURN,
+	COMPOSITE_HARD_LIGHT,
+	COMPOSITE_SOFT_LIGHT,
+	COMPOSITE_DIFFERENCE,
+	COMPOSITE_EXCLUSION,
+
+	COMPOSITE_LAST = COMPOSITE_EXCLUSION
+};
 
 /// This enumeration determines the distortion type of Distortion Effect.
 enum DistortionType

tests/Clip.cpp

@@ -42,6 +42,7 @@ TEST_CASE( "default constructor", "[libopenshot][clip]" )
 	CHECK(c1.anchor == ANCHOR_CANVAS);
 	CHECK(c1.gravity == GRAVITY_CENTER);
 	CHECK(c1.scale == SCALE_FIT);
+	CHECK(c1.composite == COMPOSITE_SOURCE_OVER);
 	CHECK(c1.Layer() == 0);
 	CHECK(c1.Position() == Approx(0.0f).margin(0.00001));
 	CHECK(c1.Start() == Approx(0.0f).margin(0.00001));
@@ -60,6 +61,7 @@ TEST_CASE( "path string constructor", "[libopenshot][clip]" )
 	CHECK(c1.anchor == ANCHOR_CANVAS);
 	CHECK(c1.gravity == GRAVITY_CENTER);
 	CHECK(c1.scale == SCALE_FIT);
+	CHECK(c1.composite == COMPOSITE_SOURCE_OVER);
 	CHECK(c1.Layer() == 0);
 	CHECK(c1.Position() == Approx(0.0f).margin(0.00001));
 	CHECK(c1.Start() == Approx(0.0f).margin(0.00001));
@@ -76,6 +78,7 @@ TEST_CASE( "basic getters and setters", "[libopenshot][clip]" )
 	CHECK(c1.anchor == ANCHOR_CANVAS);
 	CHECK(c1.gravity == GRAVITY_CENTER);
 	CHECK(c1.scale == SCALE_FIT);
+	CHECK(c1.composite == COMPOSITE_SOURCE_OVER);
 	CHECK(c1.Layer() == 0);
 	CHECK(c1.Position() == Approx(0.0f).margin(0.00001));
 	CHECK(c1.Start() == Approx(0.0f).margin(0.00001));
@@ -541,9 +544,9 @@ TEST_CASE( "painter_opacity_applied_no_per_pixel_mutation", "[libopenshot][clip]
 	// In Qt, pixelColor() returns unpremultiplied values, so expect alpha ≈ 127 and red ≈ 255.
 	QColor p = img->pixelColor(70, 50);
 	CHECK(p.alpha() == Approx(127).margin(10));
-	CHECK(p.red()   == Approx(255).margin(2));
+	CHECK(p.red()	== Approx(255).margin(2));
 	CHECK(p.green() == Approx(0).margin(2));
-	CHECK(p.blue()  == Approx(0).margin(2));
+	CHECK(p.blue()	== Approx(0).margin(2));
 }
 
 TEST_CASE( "composite_over_opaque_background_blend", "[libopenshot][clip][pr]" )
@@ -652,9 +655,9 @@ TEST_CASE( "transform_path_identity_vs_scaled", "[libopenshot][clip][pr]" )
 		REQUIRE(img);
 		// Pick a mid pixel that is white in the grid (multiple of 4)
 		QColor c = img->pixelColor(20, 20);
-		CHECK(c.red()   >= 240);
+		CHECK(c.red()	>= 240);
 		CHECK(c.green() >= 240);
-		CHECK(c.blue()  >= 240);
+		CHECK(c.blue()	>= 240);
 	}
 
 	// Case B: Downscale (trigger transform path). Clear the clip cache so we don't
@@ -684,7 +687,7 @@ TEST_CASE( "transform_path_identity_vs_scaled", "[libopenshot][clip][pr]" )
 
 		// Optional diagnostic: scaled typically yields <= number of pure whites vs identity.
 		int white_id = count_white(*out_identity->GetImage(), x0, y0, x1, y1);
-		int white_sc = count_white(*img_scaled,            x0, y0, x1, y1);
+		int white_sc = count_white(*img_scaled,		   x0, y0, x1, y1);
 		CHECK(white_sc <= white_id);
 	}
 }