使用着色器将NV12转换为RGB24的OpenGL实现

Question

我尝试编写一个应用程序，在OpenGL中显示YUV图像。使用这个片段(来源)，我成功地将YUV转换为RGB。

static long int crv_tab[256];   
static long int cbu_tab[256];   
static long int cgu_tab[256];   
static long int cgv_tab[256];   
static long int tab_76309[256]; 
static unsigned char clp[1024];   //for clip in CCIR601   

void init_yuv420p_table() 
{   
    long int crv,cbu,cgu,cgv;   
    int i,ind;      
    static int init = 0;

    if (init == 1) return;

    crv = 104597; cbu = 132201;  /* fra matrise i global.h */   
    cgu = 25675;  cgv = 53279;   

    for (i = 0; i < 256; i++)    
    {   
        crv_tab[i] = (i-128) * crv;   
        cbu_tab[i] = (i-128) * cbu;   
        cgu_tab[i] = (i-128) * cgu;   
        cgv_tab[i] = (i-128) * cgv;   
        tab_76309[i] = 76309*(i-16);   
    }   

    for (i = 0; i < 384; i++)   
        clp[i] = 0;   
    ind = 384;   
    for (i = 0;i < 256; i++)   
        clp[ind++] = i;   
    ind = 640;   
    for (i = 0;i < 384; i++)   
        clp[ind++] = 255;

    init = 1;
}

void yuv420sp_to_rgb24(YUV_TYPE type, unsigned char* yuvbuffer,unsigned char* rgbbuffer, int width,int height)   
{
    int y1, y2, u, v;    
    unsigned char *py1, *py2;   
    int i, j, c1, c2, c3, c4;   
    unsigned char *d1, *d2;   
    unsigned char *src_u;
    static int init_yuv420p = 0;

    src_u = yuvbuffer + width * height;   // u

    py1 = yuvbuffer;   // y
    py2 = py1 + width;   
    d1 = rgbbuffer;   
    d2 = d1 + 3 * width;   

    init_yuv420p_table();

    for (j = 0; j < height; j += 2)    
    {    
        for (i = 0; i < width; i += 2)    
        {
            if (type ==  FMT_NV12)
            {
                u = *src_u++;   
                v = *src_u++;      // v紧跟u，在u的下一个位置
            }
            if (type == FMT_NV21)
            {
                v = *src_u++;   
                u = *src_u++;      // u紧跟v，在v的下一个位置
            }

            c1 = crv_tab[v];   
            c2 = cgu_tab[u];   
            c3 = cgv_tab[v];   
            c4 = cbu_tab[u];   

            //up-left   
            y1 = tab_76309[*py1++];    
            *d1++ = clp[384+((y1 + c1)>>16)];     
            *d1++ = clp[384+((y1 - c2 - c3)>>16)];   
            *d1++ = clp[384+((y1 + c4)>>16)];   

            //down-left   
            y2 = tab_76309[*py2++];   
            *d2++ = clp[384+((y2 + c1)>>16)];     
            *d2++ = clp[384+((y2 - c2 - c3)>>16)];   
            *d2++ = clp[384+((y2 + c4)>>16)];   

            //up-right   
            y1 = tab_76309[*py1++];   
            *d1++ = clp[384+((y1 + c1)>>16)];     
            *d1++ = clp[384+((y1 - c2 - c3)>>16)];   
            *d1++ = clp[384+((y1 + c4)>>16)];   

            //down-right   
            y2 = tab_76309[*py2++];   
            *d2++ = clp[384+((y2 + c1)>>16)];     
            *d2++ = clp[384+((y2 - c2 - c3)>>16)];   
            *d2++ = clp[384+((y2 + c4)>>16)];   
        }
        d1  += 3*width;
        d2  += 3*width;
        py1 += width;
        py2 += width;
    }
}

为了使我的应用程序运行更加流畅，我使用片元着色器进行转换，而不是在 CPU 上执行。我将 YUV 缓冲区分成 Y_Buffer[width*height]、U_Buffer[width*height/4] 和 V_Buffer[width*height/4]，从交织的 UV_Buffer[width*height/2] 中分离出来并传递给片元着色器。（我打算使用 glTexImage2D 函数将 Y_Buffer 和 UV_Buffer 以 GL_RED 和 GL_RG 类型传递，但是在片元着色器中读取 UV_Texture 的 G 通道时，它总是返回 0）。下面是片元着色器中的转换代码：

uniform sampler2D textureY;
uniform sampler2D textureU;
uniform sampler2D textureV;
void main() {
    vec3 yuv, rgb;
    vec3 yuv2r = vec3(1.164, 0.0, 1.596);
    vec3 yuv2g = vec3(1.164, -0.391, -0.813);
    vec3 yuv2b = vec3(1.164, 2.018, 0.0);

    yuv.x = texture(textureY, texCoord).r - 0.0625;
    yuv.y = texture(textureU, texCoord).r - 0.5;
    yuv.z = texture(textureV, texCoord).r - 0.5;

    rgb.x = dot(yuv, yuv2r);
    rgb.y = dot(yuv, yuv2g);
    rgb.z = dot(yuv, yuv2b);

    FragColor = vec4(rgb, 1.0);
}

但我得到的只是绿色和粉色的像素。我在OpenGL方面还是个新手。有人能指出我可能错在哪里吗？感谢您的帮助。

更新：添加加载纹理的代码。

FILE fp = fopen("nv21.raw", "rb");
unsigned char *yuvBuffer = new unsigned char[width*height*3/2];
fread(yuvBuffer, 1, width*height*3/2, fp);

unsigned char *vuBuffer = &yuvBuffer[width*height];

int bufSize = width*height/4;
unsigned char *uBuffer = new unsigned char[bufSize];
memset(uBuffer, 0, bufSize);
unsigned char *vBuffer = new unsigned char[bufSize];
memset(vBuffer, 0, bufSize);

unsigned char *uPtr, *vPtr;
uPtr = uBuffer;
vPtr = vBuffer;

for (int i = 0; i < bufSize; i++)
{
    *vPtr = *vuBuffer++;
    *uPtr = *vuBuffer++;
}

GLuint textureID[3];

glGenTextures(1, &textureID[0]);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, textureID[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(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);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width, height, 0, GL_RED, GL_UNSIGNED_BYTE, &yuvBuffer[0]);
glBindTexture(0);

glGenTextures(1, &textureID[1]);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, textureID[1]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(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);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width/2, height/2, 0, GL_RED, GL_UNSIGNED_BYTE, uBuffer);
glBindTexture(0);

glGenTextures(1, &textureID[2]);
glActiveTexture(GL_TEXTURE2);
glBindTexture(GL_TEXTURE_2D, textureID[2]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(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);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width/2, height/2, 0, GL_RED, GL_UNSIGNED_BYTE, vBuffer);
glBindTexture(0);

- doudev

---

@Rabbid76 glActiveTexture(GL_TEXTURE0), glActiveTexture(GL_TEXTURE1), glActiveTexture(GL_TEXTURE2) 将分别与 textureY, textureU, textureV 在OpenGL中进行关联。 - doudev

@Rabbid76 抱歉，应该是 width/2 和 height/2 - doudev

@Rabbid76 哇塞，太感谢了，这个问题困扰我好几个小时了。你能写一个答案吗？我会接受它的。 - doudev

为什么标题是NV12？那段代码看起来像是YUV420。 - Trương Quốc Khánh

@TrươngQuốcKhánh 这基本上是一样的。只是可能有不同的交错方式 - doudev

Answer 1

默认情况下，着色器程序中的纹理采样器与纹理单元0相关联（默认值为0）。
您需要通过 glUniform1i 分配纹理单元的索引到纹理采样器 uniform 变量上。纹理单元是 Sampler 和 Texture 对象之间的绑定点。例如：

GLint locTexY = glGetUniformLocation(program, "textureY");
GLint locTexU = glGetUniformLocation(program, "textureU");
GLint locTexV = glGetUniformLocation(program, "textureV");

glUseProgram(program);
glUniform1i(locTexY, 0); // corresponds to GL_TEXTURE0
glUniform1i(locTexU, 1); // corresponds to GL_TEXTURE1
glUniform1i(locTexV, 2); // corresponds to GL_TEXTURE2

---

自OpenGL 4.20以来，可以通过布局限定符在着色器中设置绑定点。

layout(binding = 0) uniform sampler2D textureY;
layout(binding = 1) uniform sampler2D textureU;
layout(binding = 2) uniform sampler2D textureV;

- Rabbid76