LibGL: Implement glAlphaFunc()

This implements glAlphaFunc() for setting alpha test func and ref value
and also allows enabling and disabling GL_ALPHA_TEST

Userland/Libraries/LibGL/GL/gl.h

@@ -29,6 +29,16 @@ extern "C" {
 #define GL_TRIANGLE_STRIP 0x0103
 #define GL_POLYGON 0x0104
 
+// Depth buffer and alpha test compare functions
+#define GL_NEVER 0x0200
+#define GL_LESS 0x0201
+#define GL_EQUAL 0x0202
+#define GL_LEQUAL 0x0203
+#define GL_GREATER 0x0204
+#define GL_NOTEQUAL 0x0205
+#define GL_GEQUAL 0x0206
+#define GL_ALWAYS 0x0207
+
 // Buffer bits
 #define GL_COLOR_BUFFER_BIT 0x0200
 #define GL_DEPTH_BUFFER_BIT 0x0400
@@ -36,6 +46,13 @@ extern "C" {
 // Enable capabilities
 #define GL_CULL_FACE 0x0B44
 #define GL_DEPTH_TEST 0x0B71
+
+// Alpha testing
+#define GL_ALPHA_TEST 0x0BC0
+#define GL_ALPHA_TEST_REF 0x0BC2
+#define GL_ALPHA_TEST_FUNC 0x0BC1
+
+// Alpha blending
 #define GL_BLEND 0x0BE2
 
 // Utility
@@ -43,7 +60,7 @@ extern "C" {
 #define GL_RENDERER 0x1F01
 #define GL_VERSION 0x1F02
 
-/* Blend factors */
+// Blend factors
 #define GL_ZERO 0
 #define GL_ONE 1
 #define GL_SRC_COLOR 0x0300
@@ -152,6 +169,7 @@ GLAPI void glFlush();
 GLAPI void glFinish();
 GLAPI void glBlendFunc(GLenum sfactor, GLenum dfactor);
 GLAPI void glShadeModel(GLenum mode);
+GLAPI void glAlphaFunc(GLenum func, GLclampf ref);
 
 #ifdef __cplusplus
 }

Userland/Libraries/LibGL/GLBlend.cpp

@@ -13,3 +13,8 @@ void glBlendFunc(GLenum sfactor, GLenum dfactor)
 {
     return g_gl_context->gl_blend_func(sfactor, dfactor);
 }
+
+void glAlphaFunc(GLenum func, GLclampf ref)
+{
+    return g_gl_context->gl_alpha_func(func, ref);
+}

Userland/Libraries/LibGL/GLContext.h

@@ -51,6 +51,7 @@ public:
     virtual void gl_finish() = 0;
     virtual void gl_blend_func(GLenum src_factor, GLenum dst_factor) = 0;
     virtual void gl_shade_model(GLenum mode) = 0;
+    virtual void gl_alpha_func(GLenum func, GLclampf ref) = 0;
 
     virtual void present() = 0;
 };

Userland/Libraries/LibGL/SoftwareGLContext.cpp

@@ -688,6 +688,11 @@ void SoftwareGLContext::gl_enable(GLenum capability)
         rasterizer_options.enable_blending = true;
         update_rasterizer_options = true;
         break;
+    case GL_ALPHA_TEST:
+        m_alpha_test_enabled = true;
+        rasterizer_options.enable_alpha_test = true;
+        update_rasterizer_options = true;
+        break;
     default:
         m_error = GL_INVALID_ENUM;
         break;
@@ -723,6 +728,11 @@ void SoftwareGLContext::gl_disable(GLenum capability)
         rasterizer_options.enable_blending = false;
         update_rasterizer_options = false;
         break;
+    case GL_ALPHA_TEST:
+        m_alpha_test_enabled = false;
+        rasterizer_options.enable_alpha_test = false;
+        update_rasterizer_options = false;
+        break;
     default:
         m_error = GL_INVALID_ENUM;
         break;
@@ -946,6 +956,29 @@ void SoftwareGLContext::gl_shade_model(GLenum mode)
     m_rasterizer.set_options(options);
 }
 
+void SoftwareGLContext::gl_alpha_func(GLenum func, GLclampf ref)
+{
+    APPEND_TO_CALL_LIST_AND_RETURN_IF_NEEDED(gl_alpha_func, func, ref);
+
+    if (m_in_draw_state) {
+        m_error = GL_INVALID_OPERATION;
+        return;
+    }
+
+    if (func < GL_NEVER || func > GL_ALWAYS) {
+        m_error = GL_INVALID_ENUM;
+        return;
+    }
+
+    m_alpha_test_func = func;
+    m_alpha_test_ref_value = ref;
+
+    auto options = m_rasterizer.options();
+    options.alpha_test_func = m_alpha_test_func;
+    options.alpha_test_ref_value = m_alpha_test_ref_value;
+    m_rasterizer.set_options(options);
+}
+
 void SoftwareGLContext::present()
 {
     m_rasterizer.blit_to(*m_frontbuffer);

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -57,6 +57,7 @@ public:
     virtual void gl_finish() override;
     virtual void gl_blend_func(GLenum src_factor, GLenum dst_factor) override;
     virtual void gl_shade_model(GLenum mode) override;
+    virtual void gl_alpha_func(GLenum func, GLclampf ref) override;
 
     virtual void present() override;
 
@@ -111,6 +112,10 @@ private:
     GLenum m_blend_source_factor = GL_ONE;
     GLenum m_blend_destination_factor = GL_ZERO;
 
+    bool m_alpha_test_enabled = false;
+    GLenum m_alpha_test_func = GL_ALWAYS;
+    GLclampf m_alpha_test_ref_value = 0;
+
     NonnullRefPtr<Gfx::Bitmap> m_frontbuffer;
 
     Clipper m_clipper;
@@ -164,7 +169,8 @@ private:
             decltype(&SoftwareGLContext::gl_cull_face),
             decltype(&SoftwareGLContext::gl_call_list),
             decltype(&SoftwareGLContext::gl_blend_func),
-            decltype(&SoftwareGLContext::gl_shade_model)>;
+            decltype(&SoftwareGLContext::gl_shade_model),
+            decltype(&SoftwareGLContext::gl_alpha_func)>;
 
         using ExtraSavedArguments = Variant<
             FloatMatrix4x4>;

Userland/Libraries/LibGL/SoftwareRasterizer.h

@@ -18,6 +18,9 @@ namespace GL {
 struct RasterizerOptions {
     bool shade_smooth { true };
     bool enable_depth_test { false };
+    bool enable_alpha_test { false };
+    GLenum alpha_test_func { GL_ALWAYS };
+    float alpha_test_ref_value { 0 };
     bool enable_blending { false };
     GLenum blend_source_factor { GL_ONE };
     GLenum blend_destination_factor { GL_ONE };