LibGL: Add software rasterizer

This is based mostly on Fabian "ryg" Giesen's 2011 blog series
"A trip through the Graphics Pipeline" and Scratchapixel's
"Rasterization: a Practical Implementation".

The rasterizer processes triangles in grid aligned 16x16 pixel blocks,
calculates barycentric coordinates and edge derivatives and interpolates
bilinearly across each block.

This will theoretically allow for better utilization of modern processor
features such as SMT and SIMD, as opposed to a classic scanline based
triangle rasterizer.

This serves as a starting point to get something on the screen.
In the future we might look into properly pipelining the main loop to
make the rasterizer more flexible, enabling us to enable/disable
certain features at the block rather than the pixel level.

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -8,7 +8,10 @@
 
 #include "GLContext.h"
 #include "GLStruct.h"
+#include "SoftwareRasterizer.h"
+#include <AK/RefPtr.h>
 #include <AK/Vector.h>
+#include <LibGfx/Bitmap.h>
 #include <LibGfx/Matrix4x4.h>
 #include <LibGfx/Vector3.h>
 
@@ -16,6 +19,8 @@ namespace GL {
 
 class SoftwareGLContext : public GLContext {
 public:
+    SoftwareGLContext(Gfx::Bitmap&);
+
     virtual void gl_begin(GLenum mode) override;
     virtual void gl_clear(GLbitfield mask) override;
     virtual void gl_clear_color(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha) override;
@@ -40,6 +45,8 @@ public:
     virtual void gl_front_face(GLenum) override;
     virtual void gl_cull_face(GLenum) override;
 
+    virtual void present() override;
+
 private:
     GLenum m_current_draw_mode;
     GLenum m_current_matrix_mode;
@@ -64,6 +71,10 @@ private:
     bool m_cull_faces = false;
     GLenum m_front_face = GL_CCW;
     GLenum m_culled_sides = GL_BACK;
+
+    NonnullRefPtr<Gfx::Bitmap> m_frontbuffer;
+
+    SoftwareRasterizer m_rasterizer;
 };
 
 }