diff --git a/gopro_8:7/unfish_gopro_8:7.glsl b/gopro_8:7/unfish_gopro_8:7.glsl
index 151e74b..810ad6a 100644
--- a/gopro_8:7/unfish_gopro_8:7.glsl
+++ b/gopro_8:7/unfish_gopro_8:7.glsl
@@ -1,12 +1,14 @@
+#version 130
 // RozK
 // Fisheye removal for GoPro 11+, 8:7 ratio, without hypersmooth
 
 #extension GL_ARB_texture_rectangle: enable
 
-// TODO: investigate
-// precision highp float;
+#undef highp // defined by Qt-OpenGl
+#define rotate_180
+//#define debug_borders
 
-// #define debug_borders
+precision highp float;
 
 // uniforms
 uniform sampler2DRect myTextureY;
@@ -35,6 +37,9 @@ vec2 sensor_to_texture;
 void initialize() {
     texture_center = myResolution * 0.5;
     texture_to_sensor = (sensor_size / myResolution) * pixel_scale;
+#ifdef rotate_180
+    texture_to_sensor *= -1.0;
+#endif
     sensor_to_texture = (myResolution / sensor_size);
 }
 
@@ -53,7 +58,7 @@ vec4 unfish_pixel(const in vec2 coord) {
 
 #ifdef debug_borders
     if (y_coord.x < 0.0 || y_coord.y < 0.0 || y_coord.x > myResolution.x || y_coord.y > myResolution.y) {
-        return vec4(1.0, 1.0, 1.0, 1.0);
+        return vec4(1.0);
     }
 #endif
 
@@ -70,7 +75,7 @@ void main() {
     initialize();
 
     vec2 coord = gl_TexCoord[0].xy;
-    vec4 pixel = vec4(0.0, 0.0, 0.0, 0.0);
+    vec4 pixel = vec4(0.0);
 
     for (int y = 0; y < subsampling; y++) {
         for (int x = 0; x < subsampling; x++) {