first build attempt

shaders/sweep.vert

@@ -0,0 +1,18 @@
+/*
+ * MIT License
+ * Author: Mark Allyn
+ *
+ * sweep.vert — fullscreen quad vertex shader used by the phosphor
+ * accumulation ping-pong pass. vTexCoord maps 1:1 to the phosphor
+ * FBO in PPI space (u=0 west, u=1 east, v=0 south, v=1 north).
+ */
+#version 330 core
+
+layout(location = 0) in vec2 aPos;  // clip-space quad [-1,+1]^2
+
+out vec2 vTexCoord;
+
+void main() {
+    gl_Position = vec4(aPos, 0.0, 1.0);
+    vTexCoord   = aPos * 0.5 + 0.5;   // [0,1]^2
+}