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.cpp

@@ -7,11 +7,14 @@
 
 #include "SoftwareGLContext.h"
 #include "GLStruct.h"
+#include "SoftwareRasterizer.h"
 #include <AK/Assertions.h>
 #include <AK/Debug.h>
 #include <AK/Format.h>
 #include <AK/QuickSort.h>
 #include <AK/Vector.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/Painter.h>
 #include <LibGfx/Vector4.h>
 #include <math.h>
 
@@ -130,6 +133,12 @@ static void clip_triangle_against_frustum(Vector<FloatVector4>& in_vec)
     }
 }
 
+SoftwareGLContext::SoftwareGLContext(Gfx::Bitmap& frontbuffer)
+    : m_frontbuffer(frontbuffer)
+    , m_rasterizer(frontbuffer.size())
+{
+}
+
 void SoftwareGLContext::gl_begin(GLenum mode)
 {
     if (m_in_draw_state) {
@@ -155,12 +164,7 @@ void SoftwareGLContext::gl_clear(GLbitfield mask)
     }
 
     if (mask & GL_COLOR_BUFFER_BIT) {
-        uint8_t r = static_cast<uint8_t>(floor(m_clear_color.x() * 255.0f));
-        uint8_t g = static_cast<uint8_t>(floor(m_clear_color.y() * 255.0f));
-        uint8_t b = static_cast<uint8_t>(floor(m_clear_color.z() * 255.0f));
-
-        uint64_t color = r << 16 | g << 8 | b;
-        (void)(color);
+        m_rasterizer.clear_color(m_clear_color);
         m_error = GL_NO_ERROR;
     } else {
         m_error = GL_INVALID_ENUM;
@@ -196,9 +200,8 @@ void SoftwareGLContext::gl_end()
     // 5.   The vertices are sorted (for the rasteriser, how are we doing this? 3Dfx did this top to bottom in terms of vertex y co-ordinates)
     // 6.   The vertices are then sent off to the rasteriser and drawn to the screen
 
-    // FIXME: Don't assume screen dimensions
-    float scr_width = 640.0f;
-    float scr_height = 480.0f;
+    float scr_width = m_frontbuffer->width();
+    float scr_height = m_frontbuffer->height();
 
     // Make sure we had a `glBegin` before this call...
     if (!m_in_draw_state) {
@@ -365,22 +368,8 @@ void SoftwareGLContext::gl_end()
     }
 
     for (size_t i = 0; i < processed_triangles.size(); i++) {
-        Vector<GLVertex> sort_vert_list;
         GLTriangle& triangle = processed_triangles.at(i);
 
-        // Now we sort the vertices by their y values. A is the vertex that has the least y value,
-        // B is the middle and C is the bottom.
-        // These are sorted in groups of 3
-        sort_vert_list.append(triangle.vertices[0]);
-        sort_vert_list.append(triangle.vertices[1]);
-        sort_vert_list.append(triangle.vertices[2]);
-
-        AK::quick_sort(sort_vert_list.begin(), sort_vert_list.end(), [](auto& a, auto& b) { return a.y < b.y; });
-
-        triangle.vertices[0] = sort_vert_list.at(0);
-        triangle.vertices[1] = sort_vert_list.at(1);
-        triangle.vertices[2] = sort_vert_list.at(2);
-
         // Let's calculate the (signed) area of the triangle
         // https://cp-algorithms.com/geometry/oriented-triangle-area.html
         float dxAB = triangle.vertices[0].x - triangle.vertices[1].x; // A.x - B.x
@@ -392,19 +381,6 @@ void SoftwareGLContext::gl_end()
         if (area == 0.0f)
             continue;
 
-        int32_t vertexAx = triangle.vertices[0].x;
-        int32_t vertexAy = triangle.vertices[0].y;
-        int32_t vertexBx = triangle.vertices[1].x;
-        int32_t vertexBy = triangle.vertices[1].y;
-        int32_t vertexCx = triangle.vertices[2].x;
-        int32_t vertexCy = triangle.vertices[2].y;
-        (void)(vertexAx);
-        (void)(vertexAy);
-        (void)(vertexBx);
-        (void)(vertexBy);
-        (void)(vertexCx);
-        (void)(vertexCy);
-        
         if (m_cull_faces) {
             bool is_front = (m_front_face == GL_CCW ? area > 0 : area < 0);
 
@@ -414,6 +390,8 @@ void SoftwareGLContext::gl_end()
             if (!is_front && (m_culled_sides == GL_BACK || m_culled_sides == GL_FRONT_AND_BACK))
                 continue;
         }
+
+        m_rasterizer.submit_triangle(triangle);
     }
 
     triangle_list.clear();
@@ -778,4 +756,9 @@ void SoftwareGLContext::gl_cull_face(GLenum cull_mode)
     m_culled_sides = cull_mode;
 }
 
+void SoftwareGLContext::present()
+{
+    m_rasterizer.blit_to(*m_frontbuffer);
+}
+
 }