Create/Update assets for version 21w08b

assets/minecraft/shaders/program/phosphor.fsh

@@ -0,0 +1,18 @@
+#version 110
+
+uniform sampler2D DiffuseSampler;
+uniform sampler2D PrevSampler;
+
+varying vec2 texCoord;
+varying vec2 oneTexel;
+
+uniform vec2 InSize;
+
+uniform vec3 Phosphor;
+
+void main() {
+    vec4 CurrTexel = texture2D(DiffuseSampler, texCoord);
+    vec4 PrevTexel = texture2D(PrevSampler, texCoord);
+
+    gl_FragColor = vec4(max(PrevTexel.rgb * Phosphor, CurrTexel.rgb), 1.0);
+}