Fix related to #30152, rainbow colours produced when loading hdr image to 3D viewport/ the Nyan cat bug.

Issue is caused by scaling for power of 2 dimensions and mipmapping that happens through GLU. It looks like the library cannot handle float colour values above 1.0 correctly. Since we are close to release I will just clamp the srgb result for now even though it will result in a small performance loss for 16 bit textures only. 

I tried a few things before that, glGenerateMipmaps + no scaling (supported for 2.0 GL hardware and up), or using our own scaling instead of glu among them which worked very nicely and gave a speedup too. However, since we are close to release and there may be issues with GPU mipmap generation, see:

http://www.gamedev.net/topic/495747-another-glgeneratemipmap-question/
(old discussion but better be sure than sorry)

I went for the most compatible solution. Maybe after release this can be tested if other devs agree.

2 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/imbuf/IMB_imbuf.h b/source/blender/imbuf/IMB_imbuf.h
index 996bfd35581..07f1b9e4683 100644
--- a/source/blender/imbuf/IMB_imbuf.h
+++ b/source/blender/imbuf/IMB_imbuf.h
@@ -391,6 +391,7 @@ void IMB_buffer_float_from_float(float *rect_to, const float *rect_from,
 void IMB_buffer_byte_from_byte(unsigned char *rect_to, const unsigned char *rect_from,
 	int profile_to, int profile_from, int predivide,
 	int width, int height, int stride_to, int stride_from);
+void IMB_buffer_float_clamp(float *buf, int width, int height);
 
 /**
  * Change the ordering of the color bytes pointed to by rect from
diff --git a/source/blender/imbuf/intern/divers.c b/source/blender/imbuf/intern/divers.c
index a8ca282de66..d9ec3bf60c6 100644
--- a/source/blender/imbuf/intern/divers.c
+++ b/source/blender/imbuf/intern/divers.c
@@ -742,3 +742,10 @@ void IMB_color_to_bw(ImBuf *ibuf)
 			rct[0]= rct[1]= rct[2]= rgb_to_grayscale_byte(rct);
 	}
 }
+
+void IMB_buffer_float_clamp(float *buf, int width, int height){
+	int i, total = width*height*4;
+	for(i = 0; i < total; i++){
+		buf[i] = MIN2(1.0, buf[i]);
+	}
+}