Between Snapshot 13w41b and 13w42a, Wobble shader was modified. However, there was an error in the change which breaks the shader, preventing it from working.
What I expected to happen was...:
When utilizing the Super Secret Settings button, it would eventually cycle shaders to Wobble, which could be observed.
What actually happened was...:
No shader is visible, and the console does not note that the shader has been cycled to, staying as "Blur" until pressed again and moving to the next shader instead.
Specifics on cause and how to fix:
The problem is wobble.fsh was changed between these versions to attempt to preserve the Alpha channel (Previously, it defaulted Alpha to 1.0 instead of passing the current Alpha value along, which was likely incompatible with new transparency). To do this, (among other changes) a line was changed from vec3 to vec4. However, ".rgb" was not removed from the end of this now vec4 varable, which causes it to only pass 3 (rgb) values when vec4 requires 4 values (rgba). This causes an error, breaking the shader.
This is a simple fix: Simply remove ".rgb" from the vec4 line. I have just tested this by copying the file into a resource pack and committing this change. The shader functions normally again.
Steps to Reproduce:
1. Press Super Secret Settings button until you get to Blur
2. Press again
3. F3 will still indicate Blur as the selected shader and the console will note an error
vec3 rgb = texture2D(DiffuseSampler, texCoord + offset).rgb;
vec4 rgb = texture2D(DiffuseSampler, texCoord + offset).rgb;
vec4 rgb = texture2D(DiffuseSampler, texCoord + offset);