目前，我正在尝试使用openGL绘制图像(图像经常更新，因此必须重新绘制)。以前，我将我的图像从YUV转换为RGB，然后使用这个新图像用openGL绘制。一切都很好，但转换过程不是特别快。
我现在正试图更改代码，以便在openGL着色器中处理转换。环顾四周，我发现了一些代码片段(尤其是着色器和renderImage函数的大部分)，它们帮助我获得了基线，但我似乎无法真正正确绘制图像——我看到的只是一张黑色图像。
我很可能错过了一些非常简单和重要的东西——我使用openGL的经验相当有限。如果有人能看一看，看看他们是否发现了什么错误，请告诉我。
我应该指出，我正在努力支持iOS 4.x，所以CVOpenGLESTextureCacheCreateTextureFromImage不应该可用(即使我想使用，我也不确定如何设置它)。
如有任何帮助，我们将不胜感激。以下代码-
我的顶点着色器：
attribute vec4 position;
attribute vec4 inputTextureCoordinate;
varying vec2 textureCoordinate;
void main()
{
gl_Position = position;
textureCoordinate = inputTextureCoordinate.xy;
}
片段着色器：
#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);
}
renderImage函数：
-(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];
}
}
最后，drawFrame函数：
- (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];
}
以下是我的项目"iOS版电影播放器"中的一些代码片段。
1.碎片着色器
varying highp vec2 v_texcoord;
uniform sampler2D s_texture_y;
uniform sampler2D s_texture_u;
uniform sampler2D s_texture_v;
void main() {
highp float y = texture2D(s_texture_y, v_texcoord).r;
highp float u = texture2D(s_texture_u, v_texcoord).r - 0.5;
highp float v = texture2D(s_texture_v, v_texcoord).r - 0.5;
highp float r = y + 1.402 * v;
highp float g = y - 0.344 * u - 0.714 * v;
highp float b = y + 1.772 * u;
gl_FragColor = vec4(r,g,b,1.0);
}
2.从YUV420p帧创建纹理
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(3, _textures);
const UInt8 *pixels[3] = { yuvFrame.luma.bytes, yuvFrame.chromaB.bytes, yuvFrame.chromaR.bytes };
const NSUInteger widths[3] = { frameWidth, frameWidth / 2, frameWidth / 2 };
const NSUInteger heights[3] = { frameHeight, frameHeight / 2, frameHeight / 2 };
for (int i = 0; i < 3; ++i) {
glBindTexture(GL_TEXTURE_2D, _textures[i]);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, widths[i],heights[i],0,GL_LUMINANCE,GL_UNSIGNED_BYTE,pixels[i]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
}
3.初始化顶点和纹理坐标
static const GLfloat texCoords[] = { 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f };
static const GLfloat vertices[]= {-1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f };
4.渲染帧
[EAGLContext setCurrentContext:_context];
glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
glViewport(0, 0, _backingWidth, _backingHeight);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(_program);
for (int i = 0; i < 3; ++i) {
glActiveTexture(GL_TEXTURE0 + i);
glBindTexture(GL_TEXTURE_2D, _textures[i]);
glUniform1i(_uniformSamplers[i], i);
}
glVertexAttribPointer(ATTRIBUTE_VERTEX, 2, GL_FLOAT, 0, 0, vertices);
glEnableVertexAttribArray(ATTRIBUTE_VERTEX);
glVertexAttribPointer(ATTRIBUTE_TEXCOORD, 2, GL_FLOAT, 0, 0, texCoords);
glEnableVertexAttribArray(ATTRIBUTE_TEXCOORD);
glBindRenderbuffer(GL_RENDERBUFFER, _renderbuffer);
[_context presentRenderbuffer:GL_RENDERBUFFER];
github上项目的链接。