gpu: activate backface culling on OpenGL to remain consistent with

the Direct3D backend.

src/gpu/vertexbuffer.cpp

@@ -136,6 +136,8 @@ void VertexDeclaration::DrawElements(MeshPrimitive type, int skip, int count)
         break;
     }
 #else
+    glFrontFace(GL_CCW);
+    glEnable(GL_CULL_FACE);
 #   if defined HAVE_GL_2X && !defined __APPLE__
     glEnable(GL_ALPHA_TEST);
     glAlphaFunc(GL_GEQUAL, 0.01f);

src/gradient.cpp

@@ -63,8 +63,8 @@ void Gradient::TickDraw(float seconds)
     float const vertex[] = {   0.0f,   0.0f, 0.0f,
                              640.0f,   0.0f, 0.0f,
                                0.0f, 480.0f, 0.0f,
-                               0.0f, 480.0f, 0.0f,
                              640.0f, 480.0f, 0.0f,
+                               0.0f, 480.0f, 0.0f,
                              640.0f,   0.0f, 0.0f, };
 
     float const color[] = { 0.73f, 0.85f, 0.85f, 1.0f,

src/tileset.cpp

@@ -278,36 +278,36 @@ void TileSet::BlitTile(uint32_t id, vec3 pos, int o, vec2 scale,
     {
         float tmp[10];
 
-        *vertex++ = tmp[0] = pos.x;
-        *vertex++ = tmp[1] = pos.y + dy;
-        *vertex++ = tmp[2] = pos.z + dz;
-        *texture++ = tmp[3] = tx;
-        *texture++ = tmp[4] = ty;
-
         *vertex++ = pos.x + dx;
         *vertex++ = pos.y + dy;
         *vertex++ = pos.z + dz;
         *texture++ = tx + data->tx;
         *texture++ = ty;
 
+        *vertex++ = tmp[0] = pos.x;
+        *vertex++ = tmp[1] = pos.y + dy;
+        *vertex++ = tmp[2] = pos.z + dz;
+        *texture++ = tmp[3] = tx;
+        *texture++ = tmp[4] = ty;
+
         *vertex++ = tmp[5] = pos.x + dx;
         *vertex++ = tmp[6] = pos.y;
         *vertex++ = tmp[7] = pos.z;
         *texture++ = tmp[8] = tx + data->tx;
         *texture++ = tmp[9] = ty + data->ty;
 
-        *vertex++ = tmp[0];
-        *vertex++ = tmp[1];
-        *vertex++ = tmp[2];
-        *texture++ = tmp[3];
-        *texture++ = tmp[4];
-
         *vertex++ = tmp[5];
         *vertex++ = tmp[6];
         *vertex++ = tmp[7];
         *texture++ = tmp[8];
         *texture++ = tmp[9];
 
+        *vertex++ = tmp[0];
+        *vertex++ = tmp[1];
+        *vertex++ = tmp[2];
+        *texture++ = tmp[3];
+        *texture++ = tmp[4];
+
         *vertex++ = pos.x;
         *vertex++ = pos.y;
         *vertex++ = pos.z;