Add alpha scissor

shaders/flat.frag

@@ -2,24 +2,27 @@
 
 in vec3 UV;
 
+out vec4 FragColor;
+
 struct Material {
   vec3 color;
   bool usesColor;
   sampler2D tex;
   bool usesTex;
+  float alphaScissor;
 };
 
 uniform Material material;
 
 void main() {
-  gl_FragColor = vec4(0.0);
+  FragColor = vec4(0.0);
   if (material.usesColor) {
-    gl_FragColor += vec4(material.color, 1.0);
+    FragColor += vec4(material.color, 1.0);
   }
   if (material.usesTex) {
-    gl_FragColor += texture(material.tex, UV.xy / UV.z);
+    FragColor += texture(material.tex, UV.xy / UV.z);
   }
-  if (gl_FragColor.w < 0.99) {
+  if (FragColor.w < material.alphaScissor) {
     discard;
   }
 }