diff --git a/shaders/graph/1.frag b/shaders/graph/1.frag
index b52423f..9b82d05 100644
--- a/shaders/graph/1.frag
+++ b/shaders/graph/1.frag
@@ -107,9 +107,11 @@ 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 {
diff --git a/shaders/graph/3.frag b/shaders/graph/3.frag
index 2e21a19..df549bc 100644
--- a/shaders/graph/3.frag
+++ b/shaders/graph/3.frag
@@ -12,28 +12,52 @@ out vec4 fragment; /* output */
 #include "@graph.glsl"
 #include ":graph.glsl"
 
+/* Moves toward the border of the graph, gives the
+   y coordinate of the last colored pixel */
 float get_col_height_up(float x, float oy) {
     float y = oy;
+    #if INVERT > 0
+    while (y >= 0) {
+    #else
     while (y < screen.y) {
+    #endif
         vec4 f = texelFetch(tex, ivec2(x, y), 0);
         if (f.a <= 0) {
+            #if INVERT > 0
+            y += 1;
+            #else
             y -= 1;
+            #endif
             break;
         }
+        #if INVERT > 0
+        y -= 1;
+        #else
         y += 1;
+        #endif
     }
 
     return y;
 }
 
+/* Moves toward the base of the graph, gives the
+   y coordinate of the first colored pixel */
 float get_col_height_down(float x, float oy) {
     float y = oy;
+    #if INVERT > 0
+    while (y < screen.y) {
+    #else
     while (y >= 0) {
+    #endif
         vec4 f = texelFetch(tex, ivec2(x, y), 0);
         if (f.a > 0) {
             break;
         }
+        #if INVERT > 0
+        y += 1;
+        #else
         y -= 1;
+        #endif
     }
 
     return y;
@@ -54,7 +78,7 @@ void main() {
             h2 = get_col_height_down(gl_FragCoord.x, gl_FragCoord.y);
             fragment = texelFetch(tex, ivec2(gl_FragCoord.x, h2), 0);
 
-            a_fact = clamp((h1 - gl_FragCoord.y) / abs(h2 - h1), 0.0, 1.0);
+            a_fact = clamp(abs((h1 - gl_FragCoord.y) / (h2 - h1)), 0.0, 1.0);
 
             left_done = true;
         }
@@ -65,9 +89,9 @@ void main() {
             }
             float h3 = get_col_height_up(gl_FragCoord.x + 1, gl_FragCoord.y);
 
-            a_fact = max(a_fact, clamp((h3 - gl_FragCoord.y) / abs(h2 - h3), 0.0, 1.0));
+            a_fact = max(a_fact, clamp(abs((h3 - gl_FragCoord.y) / (h2 - h3)), 0.0, 1.0));
         }
-
+        
         fragment.a *= a_fact;
 
     }
diff --git a/shaders/graph/4.frag b/shaders/graph/4.frag
deleted file mode 100644
index 4630153..0000000
--- a/shaders/graph/4.frag
+++ /dev/null
@@ -1,22 +0,0 @@
-
-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);
-}