LibGL: Only pass bound texture units to rasterizer

Before, `SoftwareRasterizer` was iterating over all 32 possible texture
units for each fragment and checking each if they're bound to a texture.

After this change, an intrusive list containing only texture units with
bound textures is passed to the rasterizer. In GLQuake, this results in
a performance improvement of ~30% (from 12 to 16 FPS in the first demo)
on my machine.

Userland/Libraries/LibGL/SoftwareGLContext.cpp

@@ -328,6 +328,12 @@ void SoftwareGLContext::gl_end()
         }
     }
 
+    m_bound_texture_units.clear();
+    for (auto& texture_unit : m_texture_units) {
+        if (texture_unit.is_bound())
+            m_bound_texture_units.append(texture_unit);
+    }
+
     for (size_t i = 0; i < processed_triangles.size(); i++) {
         GLTriangle& triangle = processed_triangles.at(i);
 
@@ -356,7 +362,7 @@ void SoftwareGLContext::gl_end()
             swap(triangle.vertices[0], triangle.vertices[1]);
         }
 
-        m_rasterizer.submit_triangle(triangle, m_texture_units);
+        m_rasterizer.submit_triangle(triangle, m_bound_texture_units);
     }
 }
 

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -234,6 +234,7 @@ private:
     HashMap<GLuint, RefPtr<Texture>> m_allocated_textures;
     Array<TextureUnit, 32> m_texture_units;
     TextureUnit* m_active_texture_unit { &m_texture_units[0] };
+    TextureUnit::BoundList m_bound_texture_units;
 
     SoftwareRasterizer m_rasterizer;
 

Userland/Libraries/LibGL/SoftwareRasterizer.cpp

@@ -494,17 +494,12 @@ SoftwareRasterizer::SoftwareRasterizer(const Gfx::IntSize& min_size)
     m_options.scissor_box = m_render_target->rect();
 }
 
-void SoftwareRasterizer::submit_triangle(const GLTriangle& triangle, const Array<TextureUnit, 32>& texture_units)
+void SoftwareRasterizer::submit_triangle(GLTriangle const& triangle, TextureUnit::BoundList const& bound_texture_units)
 {
-    rasterize_triangle(m_options, *m_render_target, *m_depth_buffer, triangle, [this, &texture_units](const FloatVector2& uv, const FloatVector4& color, float z) -> FloatVector4 {
+    rasterize_triangle(m_options, *m_render_target, *m_depth_buffer, triangle, [this, &bound_texture_units](const FloatVector2& uv, const FloatVector4& color, float z) -> FloatVector4 {
         FloatVector4 fragment = color;
 
-        for (const auto& texture_unit : texture_units) {
-
-            // No texture is bound to this texture unit
-            if (!texture_unit.is_bound())
-                continue;
-
+        for (auto const& texture_unit : bound_texture_units) {
             // FIXME: implement GL_TEXTURE_1D, GL_TEXTURE_3D and GL_TEXTURE_CUBE_MAP
             FloatVector4 texel;
             switch (texture_unit.currently_bound_target()) {

Userland/Libraries/LibGL/SoftwareRasterizer.h

@@ -56,7 +56,7 @@ class SoftwareRasterizer final {
 public:
     SoftwareRasterizer(const Gfx::IntSize& min_size);
 
-    void submit_triangle(const GLTriangle& triangle, const Array<TextureUnit, 32>& texture_units);
+    void submit_triangle(GLTriangle const& triangle, TextureUnit::BoundList const& bound_texture_units);
     void resize(const Gfx::IntSize& min_size);
     void clear_color(const FloatVector4&);
     void clear_depth(float);

Userland/Libraries/LibGL/Tex/TextureUnit.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/IntrusiveList.h>
 #include <AK/OwnPtr.h>
 #include <LibGL/Tex/Texture2D.h>
 
@@ -35,6 +36,9 @@ public:
     bool texture_cube_map_enabled() const { return m_texture_cube_map_enabled; };
     void set_texture_cube_map_enabled(bool texture_cube_map_enabled) { m_texture_cube_map_enabled = texture_cube_map_enabled; }
 
+    IntrusiveListNode<TextureUnit> m_bound_node;
+    using BoundList = IntrusiveList<&TextureUnit::m_bound_node>;
+
 private:
     mutable RefPtr<Texture2D> m_texture_target_2d { nullptr };
     mutable RefPtr<Texture> m_currently_bound_texture { nullptr };