ios - 在 IOS 上显示 YUV(yuv420p) 不正确

Question

使用 (EAGLRenderingAPI api = kEAGLRenderingAPIOpenGLES2) 在 iOS 屏幕上显示 YUV。 但是我遇到了这个问题，以及如何处理这个问题，谢谢。

显示 YUV (size-> 3268:1838) 不正确，显示为:

但是使用相同的代码来显示 YUV(size-> 1280:720) 是正确的，显示为:

怎么了？任何帮助谢谢。

代码:

EAGLRenderingAPI api = kEAGLRenderingAPIOpenGLES2;
_context = [[EAGLContext alloc] initWithAPI:api];
if (!_context)
{
    if([LTJNYJCommon isDebug]){NSLog(@"Failed to initialize OpenGLES 2.0 context");}
    exit(1);
}

if (![EAGLContext setCurrentContext:_context])
{
    if([LTJNYJCommon isDebug]){NSLog(@"Failed to set current OpenGLES 2.0 context");}
    exit(1);
}


    int idxU = width * height;
    int idxV = idxU + (idxU / 4);
    uint8_t *pyuvData = (uint8_t *)[data bytes];

    glClearColor(0.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(x, y, w, h);
    glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, sizeof(LTGLVertex), 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer);
    glVertexAttribPointer(_texCoordSlot, 2, GL_FLOAT, GL_FALSE, sizeof(LTGLVertex), (GLvoid *)(offsetof(LTGLVertex, TexCoord)));


        //----------------------------------------------------
        //Y texture
        //----------------------------------------------------
        if (_samplerYTexture){glDeleteTextures(1, &_samplerYTexture);}
        glActiveTexture(GL_TEXTURE0);
        glGenTextures(1, &_samplerYTexture);
        glBindTexture(GL_TEXTURE_2D, _samplerYTexture);
        glUniform1i(_samplerYUniform, 0);
        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);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, width, height, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, pyuvData);
        //----------------------------------------------------
        //U texture
        //----------------------------------------------------
        if (_samplerUTexture){glDeleteTextures(1, &_samplerUTexture);}
        glActiveTexture(GL_TEXTURE1);
        glGenTextures(1, &_samplerUTexture);
        glBindTexture(GL_TEXTURE_2D, _samplerUTexture);
        glUniform1i(_samplerUUniform, 1);
        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);
        if (datalength>idxU && pyuvData[idxU]) {
            glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, width/2, height/2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, &pyuvData[idxU]);
        }else{
            if([LTJNYJCommon isDebug]){NSLog(@"error1");}
        }
        //----------------------------------------------------
        //V texture
        //----------------------------------------------------
        if (_samplerVTexture){glDeleteTextures(1, &_samplerVTexture);}
        glActiveTexture(GL_TEXTURE2);
        glGenTextures(1, &_samplerVTexture);
        glBindTexture(GL_TEXTURE_2D, _samplerVTexture);
        glUniform1i(_samplerVUniform, 2);
        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);
        if (datalength>idxV && pyuvData[idxV]) {
            glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, width/2, height/2, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, &pyuvData[idxV]);
        }else{
            if([LTJNYJCommon isDebug]){NSLog(@"error2");}
        }
        //----------------------------------------------------
        //glDrawElements
        //----------------------------------------------------
        glDrawElements(GL_TRIANGLE_STRIP, sizeof(LTGLIndices)/sizeof(GLubyte), GL_UNSIGNED_BYTE, 0);

//着色器

precision highp float;

uniform sampler2D samplerY;
uniform sampler2D samplerU;
uniform sampler2D samplerV;

varying highp vec2 TexCoordOut;

const highp mat3 yuv2rgb = mat3(1, 1, 1,
                                0, -0.39465, 2.03211,
                                1.13983, -0.58060, 0);
void main(void)
{
    highp vec3 yuv;
    yuv.x = texture2D(samplerY, TexCoordOut).r;
    yuv.y = texture2D(samplerU, TexCoordOut).r - 0.5;
    yuv.z = texture2D(samplerV, TexCoordOut).r - 0.5;

    vec3 rgb = yuv2rgb * yuv;

    gl_FragColor = vec4(rgb, 1.0);
}

//
attribute vec4 Position;
attribute vec2 TexCoordIn;

uniform mat4 Projection;
uniform mat4 Modelview;

varying vec2 TexCoordOut;

void main(void)
{
    gl_Position = Position;
    TexCoordOut = TexCoordIn;
}

Answer 1

默认情况下，OpenGL 假设图像的每一行的开始对齐 4 个字节。这是因为 GL_UNPACK_ALIGNMENT参数默认为 4。
由于图像有 1 个 (GL_LUMINANCE) channel ，大小为 1 字节，并且被紧密地打包，因此一行的开头可能未对齐。
更改 GL_UNPACK_ALIGNMENT参数为 1，在指定二维纹理图像 (glTexImage2D) 之前。

注意 glPixelStorei 改变了一个全局状态，所以在纹理图像由 glTexImage2D 指定之前设置一次参数就足够了。

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

如果你没有正确设置对齐方式，那么这会导致纹理行的偏移效果，最终图像缓冲区被越界访问。

请注意，问题是由第一个纹理的 width 3268 引起的。所以 widht/2 是 1634。1634 不能被 4 整除 (1634/4 = 408,5)。
相比之下，第二个纹理的 width 是 1280。widht/2 是 640，可以被 4 整除。
实际上对齐 2 (glPixelStorei(GL_UNPACK_ALIGNMENT, 2);) 也可以解决问题(在这种特殊情况下)。