Simplify fill;

lovr.graphics.fill renders a fullscreen quad, it's convenient because
you don't need to set up a mesh and toggle all the pipeline states.

However, if you are dealing with copying/rendering between stereo
textures, you have to write your own shader for that.  For now.

src/api/l_graphics.c

@@ -954,15 +954,7 @@ static int l_lovrGraphicsStencil(lua_State* L) {
 }
 
 static int l_lovrGraphicsFill(lua_State* L) {
-  Texture* texture = NULL;
-  if (!lua_isnoneornil(L, 1)) {
-    Canvas* canvas = luax_totype(L, 1, Canvas);
-    if (canvas) {
-      texture = lovrCanvasGetAttachments(canvas, NULL)->texture;
-    } else {
-      texture = luax_checktype(L, 1, Texture);
-    }
-  }
+  Texture* texture = lua_isnoneornil(L, 1) ? NULL : luax_checktype(L, 1, Texture);
   float u = luax_optfloat(L, 2, 0.f);
   float v = luax_optfloat(L, 3, 0.f);
   float w = luax_optfloat(L, 4, 1.f - u);

src/resources/shaders.c

@@ -247,7 +247,6 @@ const char* lovrFontFragmentShader = ""
 
 const char* lovrFillVertexShader = ""
 "vec4 position(mat4 projection, mat4 transform, vec4 vertex) { \n"
-"  texCoord.x = texCoord.x * (1. / lovrViewportCount) + (lovrViewID * 1. / float(lovrViewportCount)); \n"
 "  return vertex; \n"
 "}";