From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Sun, 31 Jan 2016 12:35:38 +0000 (+0100)
Subject: In OverlayEffect, add support for swapping the inputs.
X-Git-Tag: 1.3.0~1
X-Git-Url: https://git.sesse.net/?p=movit;a=commitdiff_plain;h=2906256567cb3899b615d45e7d8a8fb482572147

In OverlayEffect, add support for swapping the inputs.
---

diff --git a/overlay_effect.cpp b/overlay_effect.cpp
index 3a42240..3440f76 100644
--- a/overlay_effect.cpp
+++ b/overlay_effect.cpp
@@ -5,11 +5,17 @@ using namespace std;
 
 namespace movit {
 
-OverlayEffect::OverlayEffect() {}
+OverlayEffect::OverlayEffect()
+	: swap_inputs(false)
+{
+	register_int("swap_inputs", (int *)&swap_inputs);
+}
 
 string OverlayEffect::output_fragment_shader()
 {
-	return read_file("overlay_effect.frag");
+	char buf[256];
+	snprintf(buf, sizeof(buf), "#define SWAP_INPUTS %d\n", swap_inputs);
+	return buf + read_file("overlay_effect.frag");
 }
 
 }  // namespace movit
diff --git a/overlay_effect.frag b/overlay_effect.frag
index 9e5709d..d32cc06 100644
--- a/overlay_effect.frag
+++ b/overlay_effect.frag
@@ -13,7 +13,15 @@
 // C_o without the division by alpha_o).
 
 vec4 FUNCNAME(vec2 tc) {
+// SWAP_INPUTS will be #defined to 1 if we want to swap the two inputs,
+#if SWAP_INPUTS
+	vec4 bottom = INPUT2(tc);
+	vec4 top = INPUT1(tc);
+#else
 	vec4 bottom = INPUT1(tc);
 	vec4 top = INPUT2(tc);
+#endif
 	return top + (1.0 - top.a) * bottom;
 }
+
+#undef SWAP_INPUTS
diff --git a/overlay_effect.h b/overlay_effect.h
index c11569f..40a6fff 100644
--- a/overlay_effect.h
+++ b/overlay_effect.h
@@ -32,6 +32,11 @@ public:
 	// However, understanding that would require changes
 	// to EffectChain, so postpone that optimization for later.
 	virtual AlphaHandling alpha_handling() const { return INPUT_PREMULTIPLIED_ALPHA_KEEP_BLANK; }
+
+private:
+	// If true, overlays input1 on top of input2 instead of vice versa.
+	// Must be set before finalize.
+	bool swap_inputs;
 };
 
 }  // namespace movit
diff --git a/overlay_effect_test.cpp b/overlay_effect_test.cpp
index dfda93f..3f7ffd3 100644
--- a/overlay_effect_test.cpp
+++ b/overlay_effect_test.cpp
@@ -8,27 +8,36 @@
 #include "input.h"
 #include "overlay_effect.h"
 #include "test_util.h"
+#include "util.h"
 
 namespace movit {
 
 TEST(OverlayEffectTest, TopDominatesBottomWhenNoAlpha) {
-	float data_a[] = {
-		0.0f, 0.25f,
-		0.75f, 1.0f,
-	};
-	float data_b[] = {
-		1.0f, 0.5f,
-		0.75f, 0.6f,
-	};
-	float out_data[4];
-	EffectChainTester tester(data_a, 2, 2, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR);
-	Effect *input1 = tester.get_chain()->last_added_effect();
-	Effect *input2 = tester.add_input(data_b, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR);
-
-	tester.get_chain()->add_effect(new OverlayEffect(), input1, input2);
-	tester.run(out_data, GL_RED, COLORSPACE_sRGB, GAMMA_LINEAR);
-
-	expect_equal(data_b, out_data, 2, 2);
+	for (int swap_inputs = 0; swap_inputs < 2; ++swap_inputs) {  // false, true.
+		float data_a[] = {
+			0.0f, 0.25f,
+			0.75f, 1.0f,
+		};
+		float data_b[] = {
+			1.0f, 0.5f,
+			0.75f, 0.6f,
+		};
+		float out_data[4];
+		EffectChainTester tester(data_a, 2, 2, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR);
+		Effect *input1 = tester.get_chain()->last_added_effect();
+		Effect *input2 = tester.add_input(data_b, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR);
+
+		OverlayEffect *effect = new OverlayEffect();
+		CHECK(effect->set_int("swap_inputs", swap_inputs));
+		tester.get_chain()->add_effect(effect, input1, input2);
+		tester.run(out_data, GL_RED, COLORSPACE_sRGB, GAMMA_LINEAR);
+
+		if (swap_inputs) {
+			expect_equal(data_a, out_data, 2, 2);
+		} else {
+			expect_equal(data_b, out_data, 2, 2);
+		}
+	}
 }
 
 TEST(OverlayEffectTest, BottomDominatesTopWhenTopIsTransparent) {