NDK OpenGLES3.0 开发（三）：YUV 渲染

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YUV 渲染原理

前面文章一文掌握 YUV 图像的基本处理介绍了 YUV 常用的基本格式，本文以实现 NV21/NV12 的渲染为例。

前文提到，YUV 图不能直接用于显示，需要转换为 RGB 格式，而 YUV 转 RGB 是一个逐像素处理的耗时操作，在 CPU 端进行转换效率过低，这时正好可以利用 GPU 强大的并行处理能力来实现 YUV 到 RGB 的转换。

YUV 与 RGB 之间的转换公式。

需要注意的是 OpenGLES 的内置矩阵实际上是一列一列地构建的，比如 YUV 和 RGB 的转换矩阵的构建是：

mat3 convertMat = mat3(1.0, 1.0, 1.0,      //第一列
                       0.0，-0.338，1.732， //第二列
                       1.371，-0.698， 0.0);//第三列

OpenGLES 实现 YUV 渲染需要用到 GL_LUMINANCE 和 GL_LUMINANCE_ALPHA 格式的纹理，其中 GL_LUMINANCE 纹理用来加载 NV21 Y Plane 的数据，GL_LUMINANCE_ALPHA 纹理用来加载 UV Plane 的数据。

OpenGLES 常用纹理的格式类型

GL_LUMINANCE 纹理在着色器中采样的纹理像素格式是（L，L，L，1），L 表示亮度。GL_LUMINANCE 纹理在着色器中采样的纹理像素格式是（L，L，L，A），A 表示透明度。

YUV 渲染实现

YUV 渲染步骤：

• 生成 2 个纹理，编译链接着色器程序；
• 确定纹理坐标及对应的顶点坐标；
• 分别加载 NV21 的两个 Plane 数据到 2 个纹理，加载纹理坐标和顶点坐标数据到着色器程序；
• 绘制。

片段着色器脚本

#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);						
}

y_texture 和 uv_texture 分别是 NV21 Y Plane 和 UV Plane 纹理的采样器，对两个纹理采样之后组成一个（y,u,v）三维向量，之后左乘变换矩阵转换为（r,g,b）三维向量。

Java 层 Load NV21 数据

    private void LoadNV21Image() {
        InputStream is = null;
        try {
            is = getAssets().open("YUV_Image_840x1074.NV21");
        } catch (IOException e) {
            e.printStackTrace();
        }

        int lenght = 0;
        try {
            lenght = is.available();
            byte[] buffer = new byte[lenght];
            is.read(buffer);
            mGLSurfaceView.getNativeRender().native_SetImageData(IMAGE_FORMAT_NV21, 840, 1074, buffer);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try
            {
                is.close();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
        }

    }

Native 层转换为 NativeImage

void MyGLRenderContext::SetImageData(int format, int width, int height, uint8_t *pData)
{
	LOGCATE("MyGLRenderContext::SetImageData format=%d, width=%d, height=%d, pData=%p", format, width, height, pData);
	NativeImage nativeImage;
	nativeImage.format = format;
	nativeImage.width = width;
	nativeImage.height = height;
	nativeImage.ppPlane[0] = pData;

	switch (format)
	{
		case IMAGE_FORMAT_NV12:
		case IMAGE_FORMAT_NV21:
			nativeImage.ppPlane[1] = nativeImage.ppPlane[0] + width * height;
			break;
		case IMAGE_FORMAT_I420:
			nativeImage.ppPlane[1] = nativeImage.ppPlane[0] + width * height;
			nativeImage.ppPlane[2] = nativeImage.ppPlane[1] + width * height / 4;
			break;
		default:
			break;
	}

	if (m_Sample)
	{
		m_Sample->LoadImage(&nativeImage);
	}

}

//copy 到 sample
void NV21TextureMapSample::LoadImage(NativeImage *pImage)
{
	LOGCATE("NV21TextureMapSample::LoadImage pImage = %p", pImage->ppPlane[0]);
	if (pImage)
	{
		m_RenderImage.width = pImage->width;
		m_RenderImage.height = pImage->height;
		m_RenderImage.format = pImage->format;
		NativeImageUtil::CopyNativeImage(pImage, &m_RenderImage);
	}
}

加载 NV21 的 2 个 Plane 数据到纹理，ppPlane[0] 表示 Y Plane 的指针，ppPlane[1] 表示 UV Plane 的指针，注意 2 个纹理的格式和宽高。

//upload Y plane data
glBindTexture(GL_TEXTURE_2D, m_yTextureId);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, m_RenderImage.width, m_RenderImage.height, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[0]);
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);

//update UV plane data
glBindTexture(GL_TEXTURE_2D, m_uvTextureId);
glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA, m_RenderImage.width >> 1, m_RenderImage.height >> 1, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[1]);
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);

简单代码实现

// 编译链接着色器程序，生成 2 个纹理
void NV21TextureMapSample::Init()
{
	char vShaderStr[] =
			"#version 300 es                            \n"
			"layout(location = 0) in vec4 a_position;   \n"
			"layout(location = 1) in vec2 a_texCoord;   \n"
			"out vec2 v_texCoord;                       \n"
			"void main()                                \n"
			"{                                          \n"
			"   gl_Position = a_position;               \n"
			"   v_texCoord = a_texCoord;                \n"
			"}                                          \n";

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

	// Load the shaders and get a linked program object
	m_ProgramObj= GLUtils::CreateProgram(vShaderStr, fShaderStr, m_VertexShader, m_FragmentShader);

	// Get the sampler location
	m_ySamplerLoc = glGetUniformLocation (m_ProgramObj, "y_texture" );
	m_uvSamplerLoc = glGetUniformLocation(m_ProgramObj, "uv_texture");

	//create textures
	GLuint textureIds[2] = {0};
	glGenTextures(2, textureIds);

	m_yTextureId = textureIds[0];
	m_uvTextureId = textureIds[1];
}

// 加载 NV21 图像数据到纹理，加载纹理坐标和顶点坐标数据到着色器程序，绘制实现 YUV 渲染
void NV21TextureMapSample::Draw(int screenW, int screenH)
{
	LOGCATE("NV21TextureMapSample::Draw()");

	if(m_ProgramObj == GL_NONE || m_yTextureId == GL_NONE || m_uvTextureId == GL_NONE) return;

	//upload Y plane data
	glBindTexture(GL_TEXTURE_2D, m_yTextureId);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, m_RenderImage.width, m_RenderImage.height, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[0]);
	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);

	//update UV plane data
	glBindTexture(GL_TEXTURE_2D, m_uvTextureId);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA, m_RenderImage.width >> 1, m_RenderImage.height >> 1, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[1]);
	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);

	//glViewport(0, 0, m_RenderImage.width, m_RenderImage.height);

	GLfloat verticesCoords[] = {
			-1.0f,  0.78f, 0.0f,  // Position 0
			-1.0f, -0.78f, 0.0f,  // Position 1
			1.0f,  -0.78f, 0.0f,  // Position 2
			1.0f,   0.78f, 0.0f,  // Position 3
	};

	GLfloat textureCoords[] = {
			0.0f,  0.0f,        // TexCoord 0
			0.0f,  1.0f,        // TexCoord 1
			1.0f,  1.0f,        // TexCoord 2
			1.0f,  0.0f         // TexCoord 3
	};

	GLushort indices[] = { 0, 1, 2, 0, 2, 3 };

	// Use the program object
	glUseProgram (m_ProgramObj);

	// Load the vertex position
	glVertexAttribPointer (0, 3, GL_FLOAT,
						   GL_FALSE, 3 * sizeof (GLfloat), verticesCoords);
	// Load the texture coordinate
	glVertexAttribPointer (1, 2, GL_FLOAT,
						   GL_FALSE, 2 * sizeof (GLfloat), textureCoords);

	glEnableVertexAttribArray (0);
	glEnableVertexAttribArray (1);

	// Bind the Y plane map
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, m_yTextureId);

	// Set the Y plane sampler to texture unit to 0
	glUniform1i(m_ySamplerLoc, 0);

	// Bind the UV plane map
	glActiveTexture(GL_TEXTURE1);
	glBindTexture(GL_TEXTURE_2D, m_uvTextureId);

	// Set the UV plane sampler to texture unit to 1
	glUniform1i(m_uvSamplerLoc, 1);

	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);
}

YUV 渲染结果

实现代码路径：
https://github.com/githubhaohao/NDK_OpenGLES_3_0

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