twn_fog.c: fog added!

src/rendering/twn_gl_15_rendering.c

@@ -666,3 +666,30 @@ void finally_render_skybox(char *paths) {
 
     glCallList(list);
 }
+
+
+void finally_apply_fog(float start, float end, float density, Color color) {
+    if (density < 0.0f || density > 1.0f)
+        log_warn("Invalid fog density given, should be in range [0..1]");
+
+    /* TODO: cache it for constant parameters, which is a common case */
+
+    glEnable(GL_FOG);
+
+    glFogf(GL_FOG_DENSITY, density);
+    glFogf(GL_FOG_START, start);
+    glFogf(GL_FOG_END, end);
+
+    float color_conv[4];
+    color_conv[0] = (float)color.r / UINT8_MAX;
+    color_conv[1] = (float)color.g / UINT8_MAX;
+    color_conv[2] = (float)color.b / UINT8_MAX;
+    color_conv[3] = (float)color.a / UINT8_MAX;
+
+    glFogfv(GL_FOG_COLOR, color_conv);
+}
+
+
+void finally_pop_fog(void) {
+    glDisable(GL_FOG);
+}