Currently, I am trying to draw an image using openGL (the image updates very often, and thus must be redrawn). Previously, I was converting my image from YUV to RGB, and then using this new image to draw with openGL. All worked fine, but the conversion process was not particularly fast.
I am now attempting to change the code so that the conversion is taken care of in the openGL shaders. After looking around, I've found a couple code snippets (particularly the shaders and the bulk of my renderImage function) that have helped me get a baseline, but I can't seem to actually get the image to draw properly - all I ever see is a black image.
It's quite likely that I'm missing something extremely simple and important - My experience with openGL is rather limited. If anyone can take a look and see if they recognize anything wrong, please let me know.
I should point out, I'm trying to support iOS 4.x, so CVOpenGLESTextureCacheCreateTextureFromImage shouldn't be usable (and I'm not really positive how to setup to use it even if I wanted to).
Any help would be appreciated. Code below -
My Vertex shader:
attribute vec4 position;
attribute vec4 inputTextureCoordinate;
varying vec2 textureCoordinate;
void main()
{
gl_Position = position;
textureCoordinate = inputTextureCoordinate.xy;
}
Fragment Shader:
#ifdef GL_ES
precision mediump float;
#endif
varying vec2 textureCoordinate;
uniform sampler2D videoFrame;
uniform sampler2D videoFrameUV;
const mat3 yuv2rgb = mat3(
1, 0, 1.2802,
1, -0.214821, -0.380589,
1, 2.127982, 0
);
void main() {
vec3 yuv = vec3(
1.1643 * (texture2D(videoFrame, textureCoordinate).r - 0.0625),
texture2D(videoFrameUV, textureCoordinate).r - 0.5,
texture2D(videoFrameUV, textureCoordinate).a - 0.5
);
vec3 rgb = yuv * yuv2rgb;
gl_FragColor = vec4(rgb, 1.0);
}
The renderImage function:
-(void)renderImage:(ImageBuffer *)image
{
if (image)
{
int bufferHeight = image->GetHeight();
int bufferWidth = image->GetWidth();
if(!imageTexture){
// Dealing with the Y portion of the YCbCr
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &imageTexture);
//Bind Y texture
glBindTexture(GL_TEXTURE_2D, imageTexture);
glUniform1i(uniforms[UNIFORM_VIDEOFRAME], 0);
// For fitting
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// This is necessary for non-power-of-two textures
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, bufferWidth, bufferHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, image->GetPlanePointer(0));
// Dealing with the CbCr potion of the YCbCr
glActiveTexture(GL_TEXTURE1);
glGenTextures(1, &imageTextureUV);
//Bind CbCr texture
glBindTexture(GL_TEXTURE_2D, imageTextureUV);
glUniform1i(uniforms[UNIFORM_VIDEOFRAMEUV], 1);
// For fitting
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// This is necessary for non-power-of-two textures
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA, bufferWidth/2, bufferHeight/2, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, image->GetPlanePointer(1));
}
[self drawFrame];
}
}
And finally, the drawFrame function:
- (void)drawFrame
{
[self setFramebuffer];
// Replace the implementation of this method to do your own custom drawing.
static const GLfloat squareVertices[] = {
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f
};
static const GLfloat textureVertices[] = {
// 1.0f, 1.0f,
// 1.0f, 0.0f,
// 0.0f, 1.0f,
// 0.0f, 0.0f,
0.0f, 1.0f,
1.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f
// 0.0f, 0.8f,
// 1.0f, 0.8f,
// 0.0f, 0.2f,
// 1.0f, 0.2f
};
static float transY = 0.0f;
if ([context API] == kEAGLRenderingAPIOpenGLES2) {
// Use shader program.
glUseProgram(program);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, imageTexture);
// Update attribute values.
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureVertices);
glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, imageTextureUV);
// Update attribute values.
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureVertices);
glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON);
// Validate program before drawing. This is a good check, but only really necessary in a debug build.
// DEBUG macro must be defined in your debug configurations if that's not already the case.
#if defined(DEBUG)
if (![self validateProgram:program]) {
NSLog(@"Failed to validate program: %d", program);
return;
}
#endif
} else {
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, (GLfloat)(sinf(transY)/2.0f), 0.0f);
transY += 0.075f;
glVertexPointer(2, GL_FLOAT, 0, squareVertices);
glEnableClientState(GL_VERTEX_ARRAY);
}
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
[self presentFramebuffer];
}
