LibGL: Implement glDrawBuffer

Userland/Libraries/LibGL/GL/gl.h

@@ -25,6 +25,7 @@ extern "C" {
 // OpenGL related `defines`
 #define GL_TRUE 1
 #define GL_FALSE 0
+#define GL_NONE 0
 
 // Matrix Modes
 #define GL_MODELVIEW 0x0050
@@ -352,6 +353,7 @@ GLAPI void glShadeModel(GLenum mode);
 GLAPI void glAlphaFunc(GLenum func, GLclampf ref);
 GLAPI void glHint(GLenum target, GLenum mode);
 GLAPI void glReadBuffer(GLenum mode);
+GLAPI void glDrawBuffer(GLenum buffer);
 GLAPI void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid* pixels);
 GLAPI void glTexImage2D(GLenum target, GLint level, GLint internalFormat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid* data);
 GLAPI void glTexCoord2f(GLfloat s, GLfloat t);

Userland/Libraries/LibGL/GLContext.h

@@ -56,6 +56,7 @@ public:
     virtual void gl_alpha_func(GLenum func, GLclampf ref) = 0;
     virtual void gl_hint(GLenum target, GLenum mode) = 0;
     virtual void gl_read_buffer(GLenum mode) = 0;
+    virtual void gl_draw_buffer(GLenum buffer) = 0;
     virtual void gl_read_pixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid* pixels) = 0;
     virtual void gl_tex_image_2d(GLenum target, GLint level, GLint internal_format, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid* data) = 0;
     virtual void gl_tex_parameter(GLenum target, GLenum pname, GLfloat param) = 0;

Userland/Libraries/LibGL/GLUtils.cpp

@@ -85,6 +85,11 @@ void glReadBuffer(GLenum mode)
     g_gl_context->gl_read_buffer(mode);
 }
 
+void glDrawBuffer(GLenum buffer)
+{
+    g_gl_context->gl_draw_buffer(buffer);
+}
+
 void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid* pixels)
 {
     g_gl_context->gl_read_pixels(x, y, width, height, format, type, pixels);

Userland/Libraries/LibGL/SoftwareGLContext.cpp

@@ -960,6 +960,46 @@ void SoftwareGLContext::gl_read_buffer(GLenum mode)
     m_current_read_buffer = mode;
 }
 
+void SoftwareGLContext::gl_draw_buffer(GLenum buffer)
+{
+    APPEND_TO_CALL_LIST_AND_RETURN_IF_NEEDED(gl_draw_buffer, buffer);
+
+    RETURN_WITH_ERROR_IF(m_in_draw_state, GL_INVALID_OPERATION);
+
+    // FIXME: Also allow aux buffers GL_AUX0 through GL_AUX3 here
+    // plus any aux buffer between 0 and GL_AUX_BUFFERS
+    RETURN_WITH_ERROR_IF(buffer != GL_NONE
+            && buffer != GL_FRONT_LEFT
+            && buffer != GL_FRONT_RIGHT
+            && buffer != GL_BACK_LEFT
+            && buffer != GL_BACK_RIGHT
+            && buffer != GL_FRONT
+            && buffer != GL_BACK
+            && buffer != GL_LEFT
+            && buffer != GL_RIGHT,
+        GL_INVALID_ENUM);
+
+    // FIXME: We do not currently have aux buffers, so make it an invalid
+    // operation to select anything but front or back buffers. Also we do
+    // not allow selecting the stereoscopic RIGHT buffers since we do not
+    // have them configured.
+    RETURN_WITH_ERROR_IF(buffer != GL_NONE
+            && buffer != GL_FRONT_LEFT
+            && buffer != GL_FRONT
+            && buffer != GL_BACK_LEFT
+            && buffer != GL_BACK
+            && buffer != GL_FRONT
+            && buffer != GL_BACK
+            && buffer != GL_LEFT,
+        GL_INVALID_OPERATION);
+
+    m_current_draw_buffer = buffer;
+
+    auto rasterizer_options = m_rasterizer.options();
+    rasterizer_options.draw_buffer = m_current_draw_buffer;
+    m_rasterizer.set_options(rasterizer_options);
+}
+
 void SoftwareGLContext::gl_read_pixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid* pixels)
 {
     RETURN_WITH_ERROR_IF(m_in_draw_state, GL_INVALID_OPERATION);

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -66,6 +66,7 @@ public:
     virtual void gl_alpha_func(GLenum func, GLclampf ref) override;
     virtual void gl_hint(GLenum target, GLenum mode) override;
     virtual void gl_read_buffer(GLenum mode) override;
+    virtual void gl_draw_buffer(GLenum buffer) override;
     virtual void gl_read_pixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, GLvoid* pixels) override;
     virtual void gl_tex_image_2d(GLenum target, GLint level, GLint internal_format, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid* data) override;
     virtual void gl_tex_parameter(GLenum target, GLenum pname, GLfloat param) override;
@@ -152,6 +153,7 @@ private:
     GLclampf m_alpha_test_ref_value = 0;
 
     GLenum m_current_read_buffer = GL_BACK;
+    GLenum m_current_draw_buffer = GL_BACK;
 
     // Client side arrays
     bool m_client_side_vertex_array_enabled = false;

Userland/Libraries/LibGL/SoftwareRasterizer.cpp

@@ -334,7 +334,7 @@ static void rasterize_triangle(const RasterizerOptions& options, Gfx::Bitmap& re
             }
 
             // We will not update the color buffer at all
-            if (!options.color_mask)
+            if (!options.color_mask || options.draw_buffer == GL_NONE)
                 continue;
 
             // Draw the pixels according to the previously generated mask

Userland/Libraries/LibGL/SoftwareRasterizer.h

@@ -44,6 +44,7 @@ struct RasterizerOptions {
     GLboolean fog_enabled { false };
     GLfloat fog_start { 0.0f };
     GLfloat fog_end { 1.0f };
+    GLenum draw_buffer { GL_BACK };
 };
 
 class SoftwareRasterizer final {