working 6-stage fragments

shaders/frag2.glsl

@@ -0,0 +1,19 @@
+#version 460
+
+uniform float iTime;
+uniform vec2 iResolution;
+
+uniform sampler2D frame0;
+uniform sampler2D frame2;
+
+in vec2 vUV;
+layout(location = 4) out vec3 fragColor;
+
+// SRC B
+// ---------
+// IN: 0 / 2
+// OUT: 4
+
+void main() {
+    fragColor = vec3(vUV, 0.0) * step(0.3, vUV.x) * step(-0.4, -vUV.x);
+}