使用 OpenGL 实现 RGB 到 YUV 的图像格式转换

https://www.elecard.com/products/video-analysis/yuv-viewer

(0  ~  3) Y00  Y01  Y02  Y03  
(4  ~  7) Y10  Y11  Y12  Y13  
(8  ~ 11) Y20  Y21  Y22  Y23  
(12 ~ 15) Y30  Y31  Y32  Y33  

(16 ~ 19) V00  U00  V01  U01 
(20 ~ 23) V10  U10  V11  U11

#version 300 es                                     
precision mediump float;                            
in vec2 v_texCoord;                                 
layout(location = 0) out vec4 outColor;             
uniform sampler2D y_texture;                        
uniform sampler2D uv_texture;                        
void main()                                         
{                                                   
vec3 yuv;										
yuv.x = texture(y_texture, v_texCoord).r;  	
yuv.y = texture(uv_texture, v_texCoord).a-0.5;	
yuv.z = texture(uv_texture, v_texCoord).r-0.5;	
vec3 rgb =mat3( 1.0,       1.0,       	1.0,					
                0.0, 		-0.344, 	1.770,					
                1.403,  -0.714,       0.0) * yuv; 			
outColor = vec4(rgb, 1);						
}

#version 300 es
precision mediump float;
in vec2 v_texCoord;
layout(location = 0) out vec4 outColor;
uniform sampler2D s_TextureMap;//RGBA 纹理
uniform float u_Offset;//采样偏移

//RGB to YUV
//Y =  0.299R + 0.587G + 0.114B
//U = -0.147R - 0.289G + 0.436B
//V =  0.615R - 0.515G - 0.100B

const vec3 COEF_Y = vec3( 0.299,  0.587,  0.114);
const vec3 COEF_U = vec3(-0.147, -0.289,  0.436);
const vec3 COEF_V = vec3( 0.615, -0.515, -0.100);

void main()
{
    vec2 texelOffset = vec2(u_Offset, 0.0);
    vec4 color0 = texture(s_TextureMap, v_texCoord);
    //偏移 offset 采样
    vec4 color1 = texture(s_TextureMap, v_texCoord + texelOffset);

    float y0 = dot(color0.rgb, COEF_Y);
    float u0 = dot(color0.rgb, COEF_U) + 0.5;
    float v0 = dot(color0.rgb, COEF_V) + 0.5;
    float y1 = dot(color1.rgb, COEF_Y);

    outColor = vec4(y0, u0, y1, v0);
}

bool RGB2YUVSample::CreateFrameBufferObj()
{
	// 创建并初始化 FBO 纹理
	glGenTextures(1, &m_FboTextureId);
	glBindTexture(GL_TEXTURE_2D, m_FboTextureId);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glBindTexture(GL_TEXTURE_2D, GL_NONE);

	// 创建并初始化 FBO
	glGenFramebuffers(1, &m_FboId);
	glBindFramebuffer(GL_FRAMEBUFFER, m_FboId);
	glBindTexture(GL_TEXTURE_2D, m_FboTextureId);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_FboTextureId, 0);
	//FBO 纹理是用来容纳 YUYV 数据，其宽度应该设置为原图的一半
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_RenderImage.width / 2, m_RenderImage.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER)!= GL_FRAMEBUFFER_COMPLETE) {
		LOGCATE("RGB2YUVSample::CreateFrameBufferObj glCheckFramebufferStatus status != GL_FRAMEBUFFER_COMPLETE");
		return false;
	}
	glBindTexture(GL_TEXTURE_2D, GL_NONE);
	glBindFramebuffer(GL_FRAMEBUFFER, GL_NONE);
	return true;

}

glBindFramebuffer(GL_FRAMEBUFFER, m_FboId);

// 渲染成 yuyv 宽度像素减半,glviewport 宽度减半
glViewport(0, 0, m_RenderImage.width / 2, m_RenderImage.height);

glUseProgram(m_FboProgramObj);
glBindVertexArray(m_VaoIds[1]);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_ImageTextureId);
glUniform1i(m_FboSamplerLoc, 0);

//参考原理图，偏移量应该设置为 1/(width / 2) * 1/2 = 1 / width; 理论上纹素的一半
float texelOffset = (float) (1.f / (float) m_RenderImage.width);
GLUtils::setFloat(m_FboProgramObj, "u_Offset", texelOffset);

glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, (const void *)0);
glBindVertexArray(0);
glBindTexture(GL_TEXTURE_2D, 0);

//YUYV buffer = width * height * 2; 转换成 YUYV 时数据量减半，注意 buffer
uint8_t *pBuffer = new uint8_t[m_RenderImage.width * m_RenderImage.height * 2];

NativeImage nativeImage = m_RenderImage;
nativeImage.format = IMAGE_FORMAT_YUYV;
nativeImage.ppPlane[0] = pBuffer;

//glReadPixels 时 width 变为原来的一半
glReadPixels(0, 0, m_RenderImage.width / 2, nativeImage.height, GL_RGBA, GL_UNSIGNED_BYTE, pBuffer);

DumpNativeImage(&nativeImage, "/sdcard/DCIM");
delete []pBuffer;

glBindFramebuffer(GL_FRAMEBUFFER, 0);

https://github.com/githubhaohao/NDK_OpenGLES_3_0