In the drawing application that I am developing, I want my user to be able to paint with a transparent brush, for example black paint on a white background should lead to gray. When more paint is applied, the resulting color will be closer to black.
However, no matter how many times I draw over a place, the resulting color is never black; in fact, it stops changing after a few lines. Photoshop says the alpha blob drawn on the left in OpenGL is max 0.8, where I expect it to be 1.
My application works by drawing a series of stamps, as in the Apple GLPaint example, to form a line. Stamps are mixed with the following function:
glBlendFuncSeparate(GL_ONE, GL_ONE_MINUS_SRC_ALPHA, GL_ONE_MINUS_DST_ALPHA, GL_ONE);
glBlendEquation(GL_FUNC_ADD);
My fragment shader:
uniform lowp sampler2D u_texture;
varying highp vec4 f_color;
void main(){
gl_FragColor = texture2D(u_texture, gl_PointCoord).aaaa*f_color*vec4(f_color.aaa, 1);
}
How to adjust blending to get full color when painting again?
Update 11/11/2013
, , , . :
glGenFramebuffers(1, &textureFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, textureFramebuffer);
glGenTextures(1, &drawingTexture);
glBindTexture(GL_TEXTURE_2D, drawingTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, pixelWidth, pixelHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
02/12/2013
Apple GLPaint, , iOS7. , iOS 7 .
GL_ONE, GL_ONE_MINUS_SRC_ALPHA
blend iOS6. iOS7 CALAyer - ?
10/07/2014
Apple GLPaint iOS7, . , : Apple GLPaint Apple iOS7