Make anti-aliasing work with invert

shaders/graph/1.frag

@@ -107,11 +107,9 @@ void render_side(in sampler1D tex, float idx) {
     float s = get_line_height(tex, idx);
 
     /* and finally set fragment color if we are in range */
-    #if INVERT > 0
-    float pos = float(screen.y) - gl_FragCoord.y;
-    #else
+
     float pos = gl_FragCoord.y;
-    #endif
+
     if (pos + 1.5 <= s) {
         fragment = COLOR;
     } else {

shaders/graph/4.frag

@@ -0,0 +1,22 @@
+
+in vec4 gl_FragCoord;
+
+#request uniform "screen" screen
+uniform ivec2 screen; /* screen dimensions */
+
+#request uniform "prev" tex
+uniform sampler2D tex;    /* screen texture    */
+
+out vec4 fragment; /* output */
+
+#include "@graph.glsl"
+#include ":graph.glsl"
+
+void main() {
+    float newy = gl_FragCoord.y;
+    #if INVERT > 0
+    newy = float(screen.y + 1) - newy;
+    #endif
+
+    fragment = texelFetch(tex, ivec2(gl_FragCoord.x, newy), 0);
+}