From 5e05605a85a15944b95d7000745446756cdcbfa8 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Sat, 12 Jan 2013 21:50:22 +0100 Subject: [PATCH] Added an overlay effect, implementing the atop effect. --- Makefile | 2 + overlay_effect.cpp | 9 +++++ overlay_effect.frag | 26 ++++++++++++ overlay_effect.h | 25 ++++++++++++ overlay_effect_test.cpp | 88 +++++++++++++++++++++++++++++++++++++++++ 5 files changed, 150 insertions(+) create mode 100644 overlay_effect.cpp create mode 100644 overlay_effect.frag create mode 100644 overlay_effect.h create mode 100644 overlay_effect_test.cpp diff --git a/Makefile b/Makefile index 8396ac6..3d0a87c 100644 --- a/Makefile +++ b/Makefile @@ -31,6 +31,7 @@ DEMO_OBJS=demo.o # Unit tests. TESTS=effect_chain_test TESTS += mix_effect_test +TESTS += overlay_effect_test TESTS += gamma_expansion_effect_test TESTS += gamma_compression_effect_test TESTS += colorspace_conversion_effect_test @@ -67,6 +68,7 @@ LIB_OBJS += diffusion_effect.o LIB_OBJS += glow_effect.o LIB_OBJS += unsharp_mask_effect.o LIB_OBJS += mix_effect.o +LIB_OBJS += overlay_effect.o LIB_OBJS += resize_effect.o LIB_OBJS += resample_effect.o LIB_OBJS += dither_effect.o diff --git a/overlay_effect.cpp b/overlay_effect.cpp new file mode 100644 index 0000000..799c359 --- /dev/null +++ b/overlay_effect.cpp @@ -0,0 +1,9 @@ +#include "overlay_effect.h" +#include "util.h" + +OverlayEffect::OverlayEffect() {} + +std::string OverlayEffect::output_fragment_shader() +{ + return read_file("overlay_effect.frag"); +} diff --git a/overlay_effect.frag b/overlay_effect.frag new file mode 100644 index 0000000..38970ea --- /dev/null +++ b/overlay_effect.frag @@ -0,0 +1,26 @@ +// If we didn't have to worry about alpha in the bottom layer, +// this would be a simple mix(). However, since people might +// compose multiple layers together and we don't really have +// any control over the order, it's better to do it right. +// +// These formulas come from Wikipedia: +// +// http://en.wikipedia.org/wiki/Alpha_compositing + +vec4 FUNCNAME(vec2 tc) { + vec4 bottom = INPUT1(tc); + vec4 top = INPUT2(tc); + float new_alpha = mix(bottom.a, 1.0, top.a); + if (new_alpha < 1e-6) { + // new_alpha = 0 only if top.a = bottom.a = 0, at least as long as + // both alphas are within range. (If they're not, the result is not + // meaningful anyway.) And if new_alpha = 0, we don't really have + // any meaningful output anyway, so just set it to zero instead of + // getting division-by-zero below. + return vec4(0.0); + } else { + vec3 premultiplied_color = mix(bottom.rgb * bottom.aaa, top.rgb, top.a); + vec3 color = premultiplied_color / new_alpha; + return vec4(color.r, color.g, color.b, new_alpha); + } +} diff --git a/overlay_effect.h b/overlay_effect.h new file mode 100644 index 0000000..06ff793 --- /dev/null +++ b/overlay_effect.h @@ -0,0 +1,25 @@ +#ifndef _OVERLAY_EFFECT_H +#define _OVERLAY_EFFECT_H 1 + +// Put one image on top of another, using alpha where appropriate. +// (If both images are the same aspect and the top image has alpha=1.0 +// for all pixels, you will not see anything of the one on the bottom.) +// +// This is the “atop” operation from Porter-Duff blending, also used +// when merging layers in e.g. GIMP or Photoshop. +// +// The first input is the bottom, and the second is the top. + +#include "effect.h" + +class OverlayEffect : public Effect { +public: + OverlayEffect(); + virtual std::string effect_type_id() const { return "OverlayEffect"; } + std::string output_fragment_shader(); + + virtual bool needs_srgb_primaries() const { return false; } + virtual unsigned num_inputs() const { return 2; } +}; + +#endif // !defined(_OVERLAY_EFFECT_H) diff --git a/overlay_effect_test.cpp b/overlay_effect_test.cpp new file mode 100644 index 0000000..009a757 --- /dev/null +++ b/overlay_effect_test.cpp @@ -0,0 +1,88 @@ +// Unit tests for OverlayEffect. + +#include "test_util.h" +#include "gtest/gtest.h" +#include "overlay_effect.h" + +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); +} + +TEST(OverlayEffectTest, BottomDominatesTopWhenTopIsTransparent) { + float data_a[] = { + 1.0f, 0.0f, 0.0f, 0.5f, + }; + float data_b[] = { + 0.5f, 0.5f, 0.5f, 0.0f, + }; + float out_data[4]; + EffectChainTester tester(data_a, 1, 1, FORMAT_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + Effect *input1 = tester.get_chain()->last_added_effect(); + Effect *input2 = tester.add_input(data_b, FORMAT_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + + tester.get_chain()->add_effect(new OverlayEffect(), input1, input2); + tester.run(out_data, GL_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + + expect_equal(data_a, out_data, 4, 1); +} + +TEST(OverlayEffectTest, ZeroAlphaBecomesAllZero) { + float data_a[] = { + 0.0f, 0.25f, 0.5f, 0.0f + }; + float data_b[] = { + 1.0f, 1.0f, 1.0f, 0.0f + }; + float expected_data[] = { + 0.0f, 0.0f, 0.0f, 0.0f + }; + float out_data[4]; + EffectChainTester tester(data_a, 1, 1, FORMAT_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + Effect *input1 = tester.get_chain()->last_added_effect(); + Effect *input2 = tester.add_input(data_b, FORMAT_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + + tester.get_chain()->add_effect(new OverlayEffect(), input1, input2); + tester.run(out_data, GL_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + + expect_equal(expected_data, out_data, 4, 1); +} + +// This is tested against what Photoshop does: (255,0,128, 0.25) over (128,255,0, 0.5) +// becomes (179,153,51, 0.63). (Actually we fudge 0.63 to 0.625, because that's +// what it should be.) +TEST(OverlayEffectTest, PhotoshopReferenceTest) { + float data_a[] = { + 128.0f/255.0f, 1.0f, 0.0f, 0.5f + }; + float data_b[] = { + 1.0f, 0.0f, 128.0f/255.0f, 0.25f + }; + float expected_data[] = { + 179.0f/255.0f, 153.0f/255.0f, 51.0f/255.0f, 0.625f + }; + float out_data[4]; + EffectChainTester tester(data_a, 1, 1, FORMAT_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + Effect *input1 = tester.get_chain()->last_added_effect(); + Effect *input2 = tester.add_input(data_b, FORMAT_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + + tester.get_chain()->add_effect(new OverlayEffect(), input1, input2); + tester.run(out_data, GL_BGRA, COLORSPACE_sRGB, GAMMA_LINEAR); + + expect_equal(expected_data, out_data, 4, 1); +} -- 2.39.2