LibGL+LibGPU+LibSoftGPU: Implement blend equations

This implements support for `glBlendEquation` and
`glBlendEquationSeparate`. These functions modify the calculation of the
resulting color in blending mode.

Tests/LibGL/TestRender.cpp

@@ -1,10 +1,11 @@
 /*
  * Copyright (c) 2021, Leon Albrecht <leon2002.la@gmail.com>
- * Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2022-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Array.h>
 #include <AK/ByteString.h>
 #include <AK/LexicalPath.h>
 #include <LibCore/File.h>
@@ -21,9 +22,9 @@
 #endif
 #define SAVE_OUTPUT false
 
-static NonnullOwnPtr<GL::GLContext> create_testing_context(int width, int height)
+static NonnullOwnPtr<GL::GLContext> create_testing_context(int width, int height, Gfx::BitmapFormat format = Gfx::BitmapFormat::BGRx8888)
 {
-    auto bitmap = MUST(Gfx::Bitmap::create(Gfx::BitmapFormat::BGRx8888, { width, height }));
+    auto bitmap = MUST(Gfx::Bitmap::create(format, { width, height }));
     auto context = MUST(GL::create_context(*bitmap));
     GL::make_context_current(context);
     return context;
@@ -317,3 +318,61 @@ TEST_CASE(0011_tex_env_combine_with_constant_color)
     context->present();
     expect_bitmap_equals_reference(context->frontbuffer(), "0011_tex_env_combine_with_constant_color"sv);
 }
+
+TEST_CASE(0012_blend_equations)
+{
+    auto context = create_testing_context(64, 64, Gfx::BitmapFormat::BGRA8888);
+
+    // Assert initial state
+    int actual_mode;
+    glGetIntegerv(GL_BLEND_EQUATION_RGB, &actual_mode);
+    EXPECT_EQ(actual_mode, GL_FUNC_ADD);
+    glGetIntegerv(GL_BLEND_EQUATION_ALPHA, &actual_mode);
+    EXPECT_EQ(actual_mode, GL_FUNC_ADD);
+
+    // Clear with alpha 0 so we get a transparent color buffer
+    glClearColor(0, 0, 0, 0);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    glColor4f(.8f, .2f, .3f, .7f);
+    glRecti(-1, -1, 1, 1);
+
+    glColor4f(.3f, .1f, .8f, .5f);
+    glEnable(GL_BLEND);
+    glBlendFunc(GL_ONE, GL_ONE);
+
+    static constexpr Array<GLenum, 5> blend_modes = {
+        GL_FUNC_ADD,
+        GL_FUNC_SUBTRACT,
+        GL_FUNC_REVERSE_SUBTRACT,
+        GL_MIN,
+        GL_MAX,
+    };
+    auto constexpr grid_size = blend_modes.size();
+    auto constexpr cell_size = 2.f / grid_size;
+    for (size_t x = 0; x < grid_size; ++x) {
+        for (size_t y = 0; y < grid_size; ++y) {
+            auto rgb_mode = blend_modes[x];
+            auto alpha_mode = blend_modes[y];
+
+            glBlendEquationSeparate(rgb_mode, alpha_mode);
+
+            glGetIntegerv(GL_BLEND_EQUATION_RGB, &actual_mode);
+            EXPECT_EQ(static_cast<GLenum>(actual_mode), rgb_mode);
+
+            glGetIntegerv(GL_BLEND_EQUATION_ALPHA, &actual_mode);
+            EXPECT_EQ(static_cast<GLenum>(actual_mode), alpha_mode);
+
+            glRectf(
+                -1.f + cell_size * static_cast<float>(x),
+                1.f - cell_size * static_cast<float>(y),
+                -1.f + cell_size * static_cast<float>(x + 1),
+                1.f - cell_size * static_cast<float>(y + 1));
+        }
+    }
+
+    EXPECT_EQ(glGetError(), 0u);
+
+    context->present();
+    expect_bitmap_equals_reference(context->frontbuffer(), "0012_blend_equations"sv);
+}

Userland/Libraries/LibGL/ContextParameter.cpp

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
- * Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2022-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -25,6 +25,10 @@ Optional<ContextParameter> GLContext::get_context_parameter(GLenum name)
     case GL_BLEND_DST:
     case GL_BLEND_DST_ALPHA:
         return ContextParameter { .type = GL_INT, .value = { .integer_value = static_cast<GLint>(m_blend_destination_factor) } };
+    case GL_BLEND_EQUATION_ALPHA:
+        return ContextParameter { .type = GL_INT, .value = { .integer_value = static_cast<GLint>(m_blend_equation_alpha) } };
+    case GL_BLEND_EQUATION_RGB:
+        return ContextParameter { .type = GL_INT, .value = { .integer_value = static_cast<GLint>(m_blend_equation_rgb) } };
     case GL_BLEND_SRC:
     case GL_BLEND_SRC_ALPHA:
         return ContextParameter { .type = GL_INT, .value = { .integer_value = static_cast<GLint>(m_blend_source_factor) } };

Userland/Libraries/LibGL/GL/gl.h

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
- * Copyright (c) 2021-2022, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2021-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -380,11 +380,18 @@ extern "C" {
 #define GL_LIGHT6 0x4006
 #define GL_LIGHT7 0x4007
 
-// More blend factors
+// Blend factors & modes
 #define GL_CONSTANT_COLOR 0x8001
 #define GL_ONE_MINUS_CONSTANT_COLOR 0x8002
 #define GL_CONSTANT_ALPHA 0x8003
 #define GL_ONE_MINUS_CONSTANT_ALPHA 0x8004
+#define GL_FUNC_ADD 0x8006
+#define GL_MIN 0x8007
+#define GL_MAX 0x8008
+#define GL_BLEND_EQUATION_RGB 0x8009
+#define GL_FUNC_SUBTRACT 0x800A
+#define GL_FUNC_REVERSE_SUBTRACT 0x800B
+#define GL_BLEND_EQUATION_ALPHA 0x883D
 
 // Points
 #define GL_POINT_SMOOTH 0x0B10

Userland/Libraries/LibGL/GLAPI.json

@@ -50,9 +50,15 @@
     },
     "BlendEquation": {
         "arguments": [
-            {"type": "GLenum", "name": "mode"}
+            {"type": "GLenum", "name": "mode"},
+            {"expression": "mode"}
         ],
-        "unimplemented": true
+        "implementation": "blend_equation_separate"
+    },
+    "BlendEquationSeparate": {
+        "arguments": [
+            {"type": "GLenum", "name": ["modeRGB", "modeAlpha"]}
+        ]
     },
     "BlendFunc": {
         "arguments": [

Userland/Libraries/LibGL/GLContext.cpp

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
- * Copyright (c) 2022-2023, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2022-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -261,6 +261,50 @@ void GLContext::gl_finish()
     // No-op since GLContext is completely synchronous at the moment
 }
 
+void GLContext::gl_blend_equation_separate(GLenum rgb_mode, GLenum alpha_mode)
+{
+    APPEND_TO_CALL_LIST_AND_RETURN_IF_NEEDED(gl_blend_equation_separate, rgb_mode, alpha_mode);
+
+    RETURN_WITH_ERROR_IF(m_in_draw_state, GL_INVALID_OPERATION);
+    RETURN_WITH_ERROR_IF(!(rgb_mode == GL_FUNC_ADD
+                             || rgb_mode == GL_FUNC_SUBTRACT
+                             || rgb_mode == GL_FUNC_REVERSE_SUBTRACT
+                             || rgb_mode == GL_MIN
+                             || rgb_mode == GL_MAX),
+        GL_INVALID_ENUM);
+    RETURN_WITH_ERROR_IF(!(alpha_mode == GL_FUNC_ADD
+                             || alpha_mode == GL_FUNC_SUBTRACT
+                             || alpha_mode == GL_FUNC_REVERSE_SUBTRACT
+                             || alpha_mode == GL_MIN
+                             || alpha_mode == GL_MAX),
+        GL_INVALID_ENUM);
+
+    m_blend_equation_rgb = rgb_mode;
+    m_blend_equation_alpha = alpha_mode;
+
+    auto map_gl_blend_equation_to_device = [](GLenum equation) constexpr {
+        switch (equation) {
+        case GL_FUNC_ADD:
+            return GPU::BlendEquation::Add;
+        case GL_FUNC_SUBTRACT:
+            return GPU::BlendEquation::Subtract;
+        case GL_FUNC_REVERSE_SUBTRACT:
+            return GPU::BlendEquation::ReverseSubtract;
+        case GL_MIN:
+            return GPU::BlendEquation::Min;
+        case GL_MAX:
+            return GPU::BlendEquation::Max;
+        default:
+            VERIFY_NOT_REACHED();
+        }
+    };
+
+    auto options = m_rasterizer->options();
+    options.blend_equation_rgb = map_gl_blend_equation_to_device(m_blend_equation_rgb);
+    options.blend_equation_alpha = map_gl_blend_equation_to_device(m_blend_equation_alpha);
+    m_rasterizer->set_options(options);
+}
+
 void GLContext::gl_blend_func(GLenum src_factor, GLenum dst_factor)
 {
     APPEND_TO_CALL_LIST_AND_RETURN_IF_NEEDED(gl_blend_func, src_factor, dst_factor);

Userland/Libraries/LibGL/GLContext.h

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
  * Copyright (c) 2021-2022, Jesse Buhagiar <jooster669@gmail.com>
- * Copyright (c) 2022-2023, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2022-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -148,6 +148,7 @@ public:
     GLboolean gl_is_list(GLuint list);
     void gl_flush();
     void gl_finish();
+    void gl_blend_equation_separate(GLenum rgb_mode, GLenum alpha_mode);
     void gl_blend_func(GLenum src_factor, GLenum dst_factor);
     void gl_shade_model(GLenum mode);
     void gl_alpha_func(GLenum func, GLclampf ref);
@@ -336,6 +337,9 @@ private:
     GLenum m_blend_source_factor = GL_ONE;
     GLenum m_blend_destination_factor = GL_ZERO;
 
+    GLenum m_blend_equation_rgb = GL_FUNC_ADD;
+    GLenum m_blend_equation_alpha = GL_FUNC_ADD;
+
     bool m_alpha_test_enabled = false;
     GLenum m_alpha_test_func = GL_ALWAYS;
     GLclampf m_alpha_test_ref_value = 0;
@@ -469,6 +473,7 @@ private:
             decltype(&GLContext::gl_cull_face),
             decltype(&GLContext::gl_call_list),
             decltype(&GLContext::gl_call_lists),
+            decltype(&GLContext::gl_blend_equation_separate),
             decltype(&GLContext::gl_blend_func),
             decltype(&GLContext::gl_shade_model),
             decltype(&GLContext::gl_alpha_func),

Userland/Libraries/LibGPU/Enums.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
+ * Copyright (c) 2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -21,6 +22,14 @@ enum class AlphaTestFunction {
     Greater,
 };
 
+enum class BlendEquation {
+    Add,
+    Subtract,
+    ReverseSubtract,
+    Min,
+    Max,
+};
+
 enum class BlendFactor {
     Zero,
     One,

Userland/Libraries/LibGPU/RasterizerOptions.h

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
- * Copyright (c) 2022, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2022-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -23,6 +23,8 @@ struct RasterizerOptions {
     AlphaTestFunction alpha_test_func { AlphaTestFunction::Always };
     float alpha_test_ref_value { 0 };
     bool enable_blending { false };
+    BlendEquation blend_equation_rgb { BlendEquation::Add };
+    BlendEquation blend_equation_alpha { BlendEquation::Add };
     BlendFactor blend_source_factor { BlendFactor::One };
     BlendFactor blend_destination_factor { BlendFactor::One };
     u32 color_mask { 0xffffffff };

Userland/Libraries/LibSoftGPU/Device.cpp

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
  * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
- * Copyright (c) 2022-2023, Jelle Raaijmakers <jelle@gmta.nl>
+ * Copyright (c) 2022-2024, Jelle Raaijmakers <jelle@gmta.nl>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -140,7 +140,7 @@ ALWAYS_INLINE static bool is_blend_factor_constant(GPU::BlendFactor blend_factor
     return (blend_factor == GPU::BlendFactor::One || blend_factor == GPU::BlendFactor::Zero);
 }
 
-// OpenGL 1.5 § 4.1.8, table 4.1
+// OpenGL 2.0 § 4.1.8, table 4.2
 ALWAYS_INLINE static Vector4<f32x4> get_blend_factor(GPU::BlendFactor blend_factor, Vector4<f32x4> const& source_color, Vector4<f32x4> const& destination_color)
 {
     switch (blend_factor) {
@@ -173,6 +173,42 @@ ALWAYS_INLINE static Vector4<f32x4> get_blend_factor(GPU::BlendFactor blend_fact
     }
 }
 
+// OpenGL 2.0 § 4.1.8, table 4.1
+ALWAYS_INLINE static Vector4<f32x4> blend_colors(
+    GPU::BlendEquation rgb_mode,
+    GPU::BlendEquation alpha_mode,
+    Vector4<f32x4> const& source,
+    Vector4<f32x4> const& source_weights,
+    Vector4<f32x4> const& destination,
+    Vector4<f32x4> const& destination_weights)
+{
+    auto apply_equation = [&](GPU::BlendEquation mode, auto source, auto source_weights, auto destination, auto destination_weights) -> auto {
+        switch (mode) {
+        case GPU::BlendEquation::Add:
+            return source * source_weights + destination * destination_weights;
+        case GPU::BlendEquation::Subtract:
+            return source * source_weights - destination * destination_weights;
+        case GPU::BlendEquation::ReverseSubtract:
+            return destination * source_weights - source * destination_weights;
+        case GPU::BlendEquation::Min:
+            return AK::min(source, destination);
+        case GPU::BlendEquation::Max:
+            return AK::max(source, destination);
+        default:
+            VERIFY_NOT_REACHED();
+        }
+    };
+
+    // Single calculation if RGB mode is the same as the alpha mode
+    if (rgb_mode == alpha_mode)
+        return apply_equation(rgb_mode, source, source_weights, destination, destination_weights);
+
+    // Split RGB/alpha calculation
+    auto rgb = apply_equation(rgb_mode, source.xyz(), source_weights.xyz(), destination.xyz(), destination_weights.xyz());
+    auto alpha = apply_equation(alpha_mode, source.w(), source_weights.w(), destination.w(), destination_weights.w());
+    return { rgb.x(), rgb.y(), rgb.z(), alpha };
+}
+
 template<typename CB1, typename CB2, typename CB3>
 ALWAYS_INLINE void Device::rasterize(Gfx::IntRect& render_bounds, CB1 set_coverage_mask, CB2 set_quad_depth, CB3 set_quad_attributes)
 {
@@ -239,16 +275,16 @@ ALWAYS_INLINE void Device::rasterize(Gfx::IntRect& render_bounds, CB1 set_covera
     auto const qy0 = render_bounds_top & ~1;
     auto const qy1 = render_bounds_bottom & ~1;
 
-    // Blend factors
+    // Blend weights
-    Vector4<f32x4> src_factor;
+    Vector4<f32x4> source_weights;
-    Vector4<f32x4> dst_factor;
+    Vector4<f32x4> destination_weights;
-    auto const src_factor_is_constant = is_blend_factor_constant(m_options.blend_source_factor);
+    auto const source_weights_are_constant = is_blend_factor_constant(m_options.blend_source_factor);
-    auto const dst_factor_is_constant = is_blend_factor_constant(m_options.blend_destination_factor);
+    auto const destination_weights_are_constant = is_blend_factor_constant(m_options.blend_destination_factor);
     if (m_options.enable_blending) {
-        if (src_factor_is_constant)
+        if (source_weights_are_constant)
-            src_factor = get_blend_factor(m_options.blend_source_factor, {}, {});
+            source_weights = get_blend_factor(m_options.blend_source_factor, {}, {});
-        if (dst_factor_is_constant)
+        if (destination_weights_are_constant)
-            dst_factor = get_blend_factor(m_options.blend_destination_factor, {}, {});
+            destination_weights = get_blend_factor(m_options.blend_destination_factor, {}, {});
     }
 
     // Rasterize all quads
@@ -436,19 +472,19 @@ ALWAYS_INLINE void Device::rasterize(Gfx::IntRect& render_bounds, CB1 set_covera
 
             auto out_color = quad.get_output_vector4(SHADER_OUTPUT_FIRST_COLOR);
 
+            // Blend color values from pixel_staging into color_buffer
             if (m_options.enable_blending) {
                 INCREASE_STATISTICS_COUNTER(g_num_pixels_blended, maskcount(quad.mask));
 
-                // Blend color values from pixel_staging into color_buffer
+                auto const& source_color = out_color;
-                auto const& src = out_color;
+                auto const destination_color = to_vec4(dst_u32);
-                auto const dst = to_vec4(dst_u32);
 
-                if (!src_factor_is_constant)
+                if (!source_weights_are_constant)
-                    src_factor = get_blend_factor(m_options.blend_source_factor, src, dst);
+                    source_weights = get_blend_factor(m_options.blend_source_factor, source_color, destination_color);
-                if (!dst_factor_is_constant)
+                if (!destination_weights_are_constant)
-                    dst_factor = get_blend_factor(m_options.blend_destination_factor, src, dst);
+                    destination_weights = get_blend_factor(m_options.blend_destination_factor, source_color, destination_color);
 
-                out_color = src * src_factor + dst * dst_factor;
+                out_color = blend_colors(m_options.blend_equation_rgb, m_options.blend_equation_alpha, source_color, source_weights, destination_color, destination_weights);
             }
 
             auto const argb32_color = to_argb32(out_color);