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.

3 files changed, 13 insertions, 1 deletions

diff --git a/source/blender/gpu/intern/gpu_draw.c b/source/blender/gpu/intern/gpu_draw.c
index 1cd79746aee..7a61ee2eebc 100644
--- a/source/blender/gpu/intern/gpu_draw.c
+++ b/source/blender/gpu/intern/gpu_draw.c
@@ -518,6 +518,8 @@ int GPU_verify_image(Image *ima, ImageUser *iuser, int tftile, int compare, int
 					IMB_buffer_float_from_float(srgb_frect, ibuf->rect_float,
 						ibuf->channels, IB_PROFILE_SRGB, ibuf->profile, 0,
 						ibuf->x, ibuf->y, ibuf->x, ibuf->x);
+					/* clamp buffer colours to 1.0 to avoid artifacts due to glu for hdr images */
+					IMB_buffer_float_clamp(srgb_frect, ibuf->x, ibuf->y);
 					frect= srgb_frect + texwinsy*ibuf->x + texwinsx;
 				}
 				else
@@ -541,6 +543,8 @@ int GPU_verify_image(Image *ima, ImageUser *iuser, int tftile, int compare, int
 					IMB_buffer_float_from_float(srgb_frect, ibuf->rect_float,
 							ibuf->channels, IB_PROFILE_SRGB, ibuf->profile, 0,
 							ibuf->x, ibuf->y, ibuf->x, ibuf->x);
+					/* clamp buffer colours to 1.0 to avoid artifacts due to glu for hdr images */
+					IMB_buffer_float_clamp(srgb_frect, ibuf->x, ibuf->y);
 				}
 				else
 					frect= ibuf->rect_float;
@@ -615,7 +619,7 @@ int GPU_verify_image(Image *ima, ImageUser *iuser, int tftile, int compare, int
 
 	if (!(gpu_get_mipmap() && mipmap)) {
 		if(use_high_bit_depth)
-			glTexImage2D(GL_TEXTURE_2D, 0,  GL_RGBA16,  rectw, recth, 0, GL_RGBA, GL_FLOAT, frect);			
+			glTexImage2D(GL_TEXTURE_2D, 0,  GL_RGBA16,  rectw, recth, 0, GL_RGBA, GL_FLOAT, frect);
 		else
 			glTexImage2D(GL_TEXTURE_2D, 0,  GL_RGBA,  rectw, recth, 0, GL_RGBA, GL_UNSIGNED_BYTE, rect);
 		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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]);
+	}
+}