diff --git a/src/gui/render/renderGL.cpp b/src/gui/render/renderGL.cpp
index e83e98b79..b3fe689d9 100644
--- a/src/gui/render/renderGL.cpp
+++ b/src/gui/render/renderGL.cpp
@@ -113,14 +113,18 @@ const char* sh_oscRender_srcF=
   "  float val3 = texture2D(oscVal,vec2(x3,1.0)).x;\n"
   "  float valmax = max(max(val1,val2),val3);\n"
   "  float valmin = min(min(val1,val2),val3);\n"
-  "  float vald = abs(valmax-valmin);\n"
+  "  float slope = abs(valmax-valmin)*uResolution.y*0.5;\n"
   "  float alpha = 0.0;\n"
   "  if (uv.y>valmin) {\n"
   "    alpha=valmax*uResolution.y*0.5-fur_fragCoord.y+uLineWidth*0.5;\n"
   "  } else {\n"
   "    alpha=fur_fragCoord.y-valmin*uResolution.y*0.5+uLineWidth*0.5;\n"
   "  }\n"
-  "  gl_FragColor = vec4(uColor.xyz,uColor.w*clamp(alpha,0.0,1.0));\n"
+  "  if (slope>1.0) {\n"
+  "    gl_FragColor = vec4(0.0,1.0,0.0,uColor.w*clamp(alpha,0.0,1.0));\n"
+  "  } else {\n"
+  "    gl_FragColor = vec4(uColor.xyz,uColor.w*clamp(alpha,0.0,1.0));\n"
+  "  }\n"
   "}\n";
 #else
 const char* sh_wipe_srcV=