rendering.c: fix sprite uv in batches, fix alpha blending of texture atlas

src/textures.c

@@ -75,6 +75,7 @@ static void add_new_atlas(struct texture_cache *cache) {
                                                   a_mask);
     SDL_FreeFormat(native_format);
 
+    SDL_SetSurfaceBlendMode(new_atlas, SDL_BLENDMODE_NONE);
     SDL_SetSurfaceRLE(new_atlas,  true);
     arrput(cache->atlas_surfaces, new_atlas);
     arrput(cache->atlas_textures, new_gl_texture());
@@ -108,7 +109,7 @@ static void upload_texture_from_surface(GLuint texture, SDL_Surface *surface) {
 
     glTexImage2D(GL_TEXTURE_2D,
                  0,
-                 GL_RGBA,
+                 GL_RGBA8,
                  surface->w,
                  surface->h,
                  0,