gl_rasterizer: Implement GL_POINT_SPRITE

OpenGL core defaults to GL_POINT_SPRITE, meanwhile on OpenGL
compatibility we have to explicitly enable it. This fixes
gl_PointCoord's behaviour.

src/video_core/engines/maxwell_3d.h

@@ -862,7 +862,11 @@ public:
 
                 float point_size;
 
-                INSERT_UNION_PADDING_WORDS(0x7);
+                INSERT_UNION_PADDING_WORDS(0x1);
+
+                u32 point_sprite_enable;
+
+                INSERT_UNION_PADDING_WORDS(0x5);
 
                 u32 zeta_enable;
 
@@ -1494,6 +1498,7 @@ ASSERT_REG_POSITION(vb_element_base, 0x50D);
 ASSERT_REG_POSITION(vb_base_instance, 0x50E);
 ASSERT_REG_POSITION(clip_distance_enabled, 0x544);
 ASSERT_REG_POSITION(point_size, 0x546);
+ASSERT_REG_POSITION(point_sprite_enable, 0x548);
 ASSERT_REG_POSITION(zeta_enable, 0x54E);
 ASSERT_REG_POSITION(multisample_control, 0x54F);
 ASSERT_REG_POSITION(condition, 0x554);

src/video_core/renderer_opengl/gl_rasterizer.cpp

@@ -1293,6 +1293,7 @@ void RasterizerOpenGL::SyncPointState() {
     // Limit the point size to 1 since nouveau sometimes sets a point size of 0 (and that's invalid
     // in OpenGL).
     state.point.program_control = regs.vp_point_size.enable != 0;
+    state.point.sprite = regs.point_sprite_enable != 0;
     state.point.size = std::max(1.0f, regs.point_size);
 }
 

src/video_core/renderer_opengl/gl_state.cpp

@@ -128,6 +128,7 @@ void OpenGLState::ApplyClipDistances() {
 
 void OpenGLState::ApplyPointSize() {
     Enable(GL_PROGRAM_POINT_SIZE, cur_state.point.program_control, point.program_control);
+    Enable(GL_POINT_SPRITE, cur_state.point.sprite, point.sprite);
     if (UpdateValue(cur_state.point.size, point.size)) {
         glPointSize(point.size);
     }

src/video_core/renderer_opengl/gl_state.h

@@ -132,6 +132,7 @@ public:
 
     struct {
         bool program_control = false; // GL_PROGRAM_POINT_SIZE
+        bool sprite = false;          // GL_POINT_SPRITE
         GLfloat size = 1.0f;          // GL_POINT_SIZE
     } point;