OpenGL ES 2.0 - Blending issue with text (iOS)











up vote
0
down vote

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I have grey shadows around texts when I blend them with OpenGL.



enter image description here



Currently, this is my blending function :



glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);


If I change it to :



glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);


It works, and I obtain the same result with Gimp :



enter image description here



But, however with GL_ONE, the text can't be faded into the background anymore. It's like it's either transparency 0 or 1.



Also with GL_ONE, a crossfade between 2 pictures will somehow make the result image super bright :



enter image description here



Whereas with GL_SRC_ALPHA it looks normal :



enter image description here



So both solutions have pros and cons. I don't want the grey shadows, but I want to keep the crossfade effect.. Any suggestions would be very appreciated.



This is my fragment shader :



gl_FragColor = (v_Color * texture2D(u_Texture, v_TexCoordinate));


And here's how the textures (text and images) are loaded (premultiplied last):



+ (GLuint)getGLTextureFromCGIImage:(CGImageRef)cgiImage {
size_t width = CGImageGetWidth(cgiImage);
size_t height = CGImageGetHeight(cgiImage);

GLubyte *spriteData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef spriteContext = CGBitmapContextCreate(spriteData,
width,
height,
bitsPerComponent,
bytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGColorSpaceRelease(colorSpace);

CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), cgiImage);
CGContextRelease(spriteContext);

return [GLMediaUtils getGLTextureFromPixelsInFormat:GL_RGBA
width:(int)width
height:(int)height
pixels:spriteData];
}

+ (GLuint)getGLTextureFromPixelsInFormat:(GLenum)format
width:(int)width
height:(int)height
pixels:(void *)pixels {

glActiveTexture(GL_TEXTURE0);

GLuint texture;
glGenTextures(1, &texture);


glBindTexture(GL_TEXTURE_2D, texture);


glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);


GLenum type = GL_UNSIGNED_BYTE;
if(format == GL_RGB) // RGB565
type = GL_UNSIGNED_SHORT_5_6_5;

glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, type, pixels);

free(pixels);
glFlush();

return texture;
}









share|improve this question




















  • 1




    what you're looking for is pre-multiplied alpha.
    – derhass
    Nov 21 at 18:39










  • @derhass Thanks but what do you mean ? The images are loaded with : "kCGImageAlphaPremultipliedLast"
    – Xys
    Nov 21 at 18:52










  • have you tried enabling multisampling when you are using GL_SRC_ALPHA?
    – Paritosh Kulkarni
    Nov 21 at 19:14

















up vote
0
down vote

favorite












I have grey shadows around texts when I blend them with OpenGL.



enter image description here



Currently, this is my blending function :



glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);


If I change it to :



glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);


It works, and I obtain the same result with Gimp :



enter image description here



But, however with GL_ONE, the text can't be faded into the background anymore. It's like it's either transparency 0 or 1.



Also with GL_ONE, a crossfade between 2 pictures will somehow make the result image super bright :



enter image description here



Whereas with GL_SRC_ALPHA it looks normal :



enter image description here



So both solutions have pros and cons. I don't want the grey shadows, but I want to keep the crossfade effect.. Any suggestions would be very appreciated.



This is my fragment shader :



gl_FragColor = (v_Color * texture2D(u_Texture, v_TexCoordinate));


And here's how the textures (text and images) are loaded (premultiplied last):



+ (GLuint)getGLTextureFromCGIImage:(CGImageRef)cgiImage {
size_t width = CGImageGetWidth(cgiImage);
size_t height = CGImageGetHeight(cgiImage);

GLubyte *spriteData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef spriteContext = CGBitmapContextCreate(spriteData,
width,
height,
bitsPerComponent,
bytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGColorSpaceRelease(colorSpace);

CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), cgiImage);
CGContextRelease(spriteContext);

return [GLMediaUtils getGLTextureFromPixelsInFormat:GL_RGBA
width:(int)width
height:(int)height
pixels:spriteData];
}

+ (GLuint)getGLTextureFromPixelsInFormat:(GLenum)format
width:(int)width
height:(int)height
pixels:(void *)pixels {

glActiveTexture(GL_TEXTURE0);

GLuint texture;
glGenTextures(1, &texture);


glBindTexture(GL_TEXTURE_2D, texture);


glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);


GLenum type = GL_UNSIGNED_BYTE;
if(format == GL_RGB) // RGB565
type = GL_UNSIGNED_SHORT_5_6_5;

glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, type, pixels);

free(pixels);
glFlush();

return texture;
}









share|improve this question




















  • 1




    what you're looking for is pre-multiplied alpha.
    – derhass
    Nov 21 at 18:39










  • @derhass Thanks but what do you mean ? The images are loaded with : "kCGImageAlphaPremultipliedLast"
    – Xys
    Nov 21 at 18:52










  • have you tried enabling multisampling when you are using GL_SRC_ALPHA?
    – Paritosh Kulkarni
    Nov 21 at 19:14















up vote
0
down vote

favorite









up vote
0
down vote

favorite











I have grey shadows around texts when I blend them with OpenGL.



enter image description here



Currently, this is my blending function :



glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);


If I change it to :



glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);


It works, and I obtain the same result with Gimp :



enter image description here



But, however with GL_ONE, the text can't be faded into the background anymore. It's like it's either transparency 0 or 1.



Also with GL_ONE, a crossfade between 2 pictures will somehow make the result image super bright :



enter image description here



Whereas with GL_SRC_ALPHA it looks normal :



enter image description here



So both solutions have pros and cons. I don't want the grey shadows, but I want to keep the crossfade effect.. Any suggestions would be very appreciated.



This is my fragment shader :



gl_FragColor = (v_Color * texture2D(u_Texture, v_TexCoordinate));


And here's how the textures (text and images) are loaded (premultiplied last):



+ (GLuint)getGLTextureFromCGIImage:(CGImageRef)cgiImage {
size_t width = CGImageGetWidth(cgiImage);
size_t height = CGImageGetHeight(cgiImage);

GLubyte *spriteData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef spriteContext = CGBitmapContextCreate(spriteData,
width,
height,
bitsPerComponent,
bytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGColorSpaceRelease(colorSpace);

CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), cgiImage);
CGContextRelease(spriteContext);

return [GLMediaUtils getGLTextureFromPixelsInFormat:GL_RGBA
width:(int)width
height:(int)height
pixels:spriteData];
}

+ (GLuint)getGLTextureFromPixelsInFormat:(GLenum)format
width:(int)width
height:(int)height
pixels:(void *)pixels {

glActiveTexture(GL_TEXTURE0);

GLuint texture;
glGenTextures(1, &texture);


glBindTexture(GL_TEXTURE_2D, texture);


glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);


GLenum type = GL_UNSIGNED_BYTE;
if(format == GL_RGB) // RGB565
type = GL_UNSIGNED_SHORT_5_6_5;

glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, type, pixels);

free(pixels);
glFlush();

return texture;
}









share|improve this question















I have grey shadows around texts when I blend them with OpenGL.



enter image description here



Currently, this is my blending function :



glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);


If I change it to :



glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);


It works, and I obtain the same result with Gimp :



enter image description here



But, however with GL_ONE, the text can't be faded into the background anymore. It's like it's either transparency 0 or 1.



Also with GL_ONE, a crossfade between 2 pictures will somehow make the result image super bright :



enter image description here



Whereas with GL_SRC_ALPHA it looks normal :



enter image description here



So both solutions have pros and cons. I don't want the grey shadows, but I want to keep the crossfade effect.. Any suggestions would be very appreciated.



This is my fragment shader :



gl_FragColor = (v_Color * texture2D(u_Texture, v_TexCoordinate));


And here's how the textures (text and images) are loaded (premultiplied last):



+ (GLuint)getGLTextureFromCGIImage:(CGImageRef)cgiImage {
size_t width = CGImageGetWidth(cgiImage);
size_t height = CGImageGetHeight(cgiImage);

GLubyte *spriteData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef spriteContext = CGBitmapContextCreate(spriteData,
width,
height,
bitsPerComponent,
bytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGColorSpaceRelease(colorSpace);

CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), cgiImage);
CGContextRelease(spriteContext);

return [GLMediaUtils getGLTextureFromPixelsInFormat:GL_RGBA
width:(int)width
height:(int)height
pixels:spriteData];
}

+ (GLuint)getGLTextureFromPixelsInFormat:(GLenum)format
width:(int)width
height:(int)height
pixels:(void *)pixels {

glActiveTexture(GL_TEXTURE0);

GLuint texture;
glGenTextures(1, &texture);


glBindTexture(GL_TEXTURE_2D, texture);


glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);


GLenum type = GL_UNSIGNED_BYTE;
if(format == GL_RGB) // RGB565
type = GL_UNSIGNED_SHORT_5_6_5;

glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, type, pixels);

free(pixels);
glFlush();

return texture;
}






ios opengl-es opengl-es-2.0 blending






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 21 at 19:47









genpfault

41.3k95197




41.3k95197










asked Nov 21 at 18:27









Xys

194116




194116








  • 1




    what you're looking for is pre-multiplied alpha.
    – derhass
    Nov 21 at 18:39










  • @derhass Thanks but what do you mean ? The images are loaded with : "kCGImageAlphaPremultipliedLast"
    – Xys
    Nov 21 at 18:52










  • have you tried enabling multisampling when you are using GL_SRC_ALPHA?
    – Paritosh Kulkarni
    Nov 21 at 19:14
















  • 1




    what you're looking for is pre-multiplied alpha.
    – derhass
    Nov 21 at 18:39










  • @derhass Thanks but what do you mean ? The images are loaded with : "kCGImageAlphaPremultipliedLast"
    – Xys
    Nov 21 at 18:52










  • have you tried enabling multisampling when you are using GL_SRC_ALPHA?
    – Paritosh Kulkarni
    Nov 21 at 19:14










1




1




what you're looking for is pre-multiplied alpha.
– derhass
Nov 21 at 18:39




what you're looking for is pre-multiplied alpha.
– derhass
Nov 21 at 18:39












@derhass Thanks but what do you mean ? The images are loaded with : "kCGImageAlphaPremultipliedLast"
– Xys
Nov 21 at 18:52




@derhass Thanks but what do you mean ? The images are loaded with : "kCGImageAlphaPremultipliedLast"
– Xys
Nov 21 at 18:52












have you tried enabling multisampling when you are using GL_SRC_ALPHA?
– Paritosh Kulkarni
Nov 21 at 19:14






have you tried enabling multisampling when you are using GL_SRC_ALPHA?
– Paritosh Kulkarni
Nov 21 at 19:14














1 Answer
1






active

oldest

votes

















up vote
1
down vote



accepted










You're almost there. You need to use pre-multiplied alpha if you want to avoid ghosting from the texture (because GL blending is post-multiplied alpha normally, which causes color bleed across the channels).



Normally GL_ONE works because the correct alpha has been pre-baked into the texture RGB color channels prior to texture upload. If you start adding custom fading on top of that in the shader then you end up with a desync between the alpha you use for blending in the shader and the alpha that was used for pre-multiplication.



... so you need to add an adjustment to your fragment shader based on the new alpha value to get back to a stable premultiplication value. Something like:



vec4 texColor = texture2D(u_Texture, v_TexCoordinate);
// Scale the texture RGB by the vertex color
texColor.rgb *= v_color.rgb;
// Scale the texture RGBA by the vertex alpha to reinstate premultiplication
gl_FragColor = texColor * v_color.a;


The other approach is to store the font as only a luminance texture. You get grey shadows because the color channels are black outside of the font and texture filtering is mixing white and black. If you know the font color is white you don't need to store RGB values in a texture at all ... (or if you are lazy just keep the existing texture and flood fill the entire texture RGB channels with white).






share|improve this answer























  • Thanks I think it solved everything !
    – Xys
    Nov 22 at 11:29











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1 Answer
1






active

oldest

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1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
1
down vote



accepted










You're almost there. You need to use pre-multiplied alpha if you want to avoid ghosting from the texture (because GL blending is post-multiplied alpha normally, which causes color bleed across the channels).



Normally GL_ONE works because the correct alpha has been pre-baked into the texture RGB color channels prior to texture upload. If you start adding custom fading on top of that in the shader then you end up with a desync between the alpha you use for blending in the shader and the alpha that was used for pre-multiplication.



... so you need to add an adjustment to your fragment shader based on the new alpha value to get back to a stable premultiplication value. Something like:



vec4 texColor = texture2D(u_Texture, v_TexCoordinate);
// Scale the texture RGB by the vertex color
texColor.rgb *= v_color.rgb;
// Scale the texture RGBA by the vertex alpha to reinstate premultiplication
gl_FragColor = texColor * v_color.a;


The other approach is to store the font as only a luminance texture. You get grey shadows because the color channels are black outside of the font and texture filtering is mixing white and black. If you know the font color is white you don't need to store RGB values in a texture at all ... (or if you are lazy just keep the existing texture and flood fill the entire texture RGB channels with white).






share|improve this answer























  • Thanks I think it solved everything !
    – Xys
    Nov 22 at 11:29















up vote
1
down vote



accepted










You're almost there. You need to use pre-multiplied alpha if you want to avoid ghosting from the texture (because GL blending is post-multiplied alpha normally, which causes color bleed across the channels).



Normally GL_ONE works because the correct alpha has been pre-baked into the texture RGB color channels prior to texture upload. If you start adding custom fading on top of that in the shader then you end up with a desync between the alpha you use for blending in the shader and the alpha that was used for pre-multiplication.



... so you need to add an adjustment to your fragment shader based on the new alpha value to get back to a stable premultiplication value. Something like:



vec4 texColor = texture2D(u_Texture, v_TexCoordinate);
// Scale the texture RGB by the vertex color
texColor.rgb *= v_color.rgb;
// Scale the texture RGBA by the vertex alpha to reinstate premultiplication
gl_FragColor = texColor * v_color.a;


The other approach is to store the font as only a luminance texture. You get grey shadows because the color channels are black outside of the font and texture filtering is mixing white and black. If you know the font color is white you don't need to store RGB values in a texture at all ... (or if you are lazy just keep the existing texture and flood fill the entire texture RGB channels with white).






share|improve this answer























  • Thanks I think it solved everything !
    – Xys
    Nov 22 at 11:29













up vote
1
down vote



accepted







up vote
1
down vote



accepted






You're almost there. You need to use pre-multiplied alpha if you want to avoid ghosting from the texture (because GL blending is post-multiplied alpha normally, which causes color bleed across the channels).



Normally GL_ONE works because the correct alpha has been pre-baked into the texture RGB color channels prior to texture upload. If you start adding custom fading on top of that in the shader then you end up with a desync between the alpha you use for blending in the shader and the alpha that was used for pre-multiplication.



... so you need to add an adjustment to your fragment shader based on the new alpha value to get back to a stable premultiplication value. Something like:



vec4 texColor = texture2D(u_Texture, v_TexCoordinate);
// Scale the texture RGB by the vertex color
texColor.rgb *= v_color.rgb;
// Scale the texture RGBA by the vertex alpha to reinstate premultiplication
gl_FragColor = texColor * v_color.a;


The other approach is to store the font as only a luminance texture. You get grey shadows because the color channels are black outside of the font and texture filtering is mixing white and black. If you know the font color is white you don't need to store RGB values in a texture at all ... (or if you are lazy just keep the existing texture and flood fill the entire texture RGB channels with white).






share|improve this answer














You're almost there. You need to use pre-multiplied alpha if you want to avoid ghosting from the texture (because GL blending is post-multiplied alpha normally, which causes color bleed across the channels).



Normally GL_ONE works because the correct alpha has been pre-baked into the texture RGB color channels prior to texture upload. If you start adding custom fading on top of that in the shader then you end up with a desync between the alpha you use for blending in the shader and the alpha that was used for pre-multiplication.



... so you need to add an adjustment to your fragment shader based on the new alpha value to get back to a stable premultiplication value. Something like:



vec4 texColor = texture2D(u_Texture, v_TexCoordinate);
// Scale the texture RGB by the vertex color
texColor.rgb *= v_color.rgb;
// Scale the texture RGBA by the vertex alpha to reinstate premultiplication
gl_FragColor = texColor * v_color.a;


The other approach is to store the font as only a luminance texture. You get grey shadows because the color channels are black outside of the font and texture filtering is mixing white and black. If you know the font color is white you don't need to store RGB values in a texture at all ... (or if you are lazy just keep the existing texture and flood fill the entire texture RGB channels with white).







share|improve this answer














share|improve this answer



share|improve this answer








edited Nov 21 at 21:32

























answered Nov 21 at 21:27









solidpixel

4,77611120




4,77611120












  • Thanks I think it solved everything !
    – Xys
    Nov 22 at 11:29


















  • Thanks I think it solved everything !
    – Xys
    Nov 22 at 11:29
















Thanks I think it solved everything !
– Xys
Nov 22 at 11:29




Thanks I think it solved everything !
– Xys
Nov 22 at 11:29


















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