optimize graphics performance

modules/game_shaders/item.frag

@@ -1,11 +1,11 @@
 uniform float opacity; // painter opacity
 uniform vec4 color; // painter color
 uniform float time; // time in seconds since shader linkage
-uniform sampler2D texture; // map texture
+uniform sampler2D tex0; // map texture
+varying vec2 texCoord; // map texture coords
 //uniform int itemId; // item id
-varying vec2 textureCoords; // map texture coords
 
 void main()
 {
-    gl_FragColor = texture2D(texture, textureCoords);
+    gl_FragColor = texture2D(tex0, texCoord);
 }