Create/Update assets for version 21w18a

assets/minecraft/shaders/program/phosphor.fsh

@@ -0,0 +1,20 @@
+#version 150
+
+uniform sampler2D DiffuseSampler;
+uniform sampler2D PrevSampler;
+
+in vec2 texCoord;
+in vec2 oneTexel;
+
+uniform vec2 InSize;
+
+uniform vec3 Phosphor;
+
+out vec4 fragColor;
+
+void main() {
+    vec4 CurrTexel = texture(DiffuseSampler, texCoord);
+    vec4 PrevTexel = texture(PrevSampler, texCoord);
+
+    fragColor = vec4(max(PrevTexel.rgb * Phosphor, CurrTexel.rgb), 1.0);
+}