objective-c - 两个 FBO 之间的乒乓渲染在第一帧后失败。

Question

我正在尝试创建两个 FBO 并实现乒乓渲染。但是，我只能让第一帧正常工作。我正在尝试模拟人生游戏，但在第一帧之后，我只看到黑屏。你能帮我检查一下吗？我在这个问题上花了几个小时。

编辑

可能我没描述清楚。其实我想用textureB做texture渲染到textureA，再用textureA渲染到screen，反之亦然。

编辑我可以看到第一帧，它是 textureB。通过片段着色器后，它变成黑色。起初，我怀疑片段着色器，我将其更改为仅将黑色恢复为白色，将白色恢复为黑色。它仍然变成全黑。

设置fbo和纹理

glEnable(GL_TEXTURE_2D);
    glGenTextures(1, &textureA);
    glBindTexture(GL_TEXTURE_2D, textureA);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_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);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 256, 256, 0, GL_RGBA,
                 GL_UNSIGNED_BYTE, NULL);

    glGenTextures(1, &textureB);
    glBindTexture(GL_TEXTURE_2D, textureB);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_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);

    data=(GLubyte*)malloc(256*256*4*sizeof(GLubyte));
    GLubyte val;
    for (int i = 0; i < 256 * 256 * 4; i+=4) {   
        if (rand()%10 ==1) 
            { val = 0; } 
        else 
            { val = 255; }
        data[i] = data[i+1] = data[i+2] = val;
        data[i+3] = 255;
    }
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);

    glGenFramebuffers(1, &fboA);
    glBindFramebuffer(GL_FRAMEBUFFER, fboA);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textureA, 0);

    glGenFramebuffers(1, &fboB);
    glBindFramebuffer(GL_FRAMEBUFFER, fboB);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textureB, 0);

渲染循环

if ([context API] == kEAGLRenderingAPIOpenGLES2) {


        if(counter%2==0)
        {
            glUseProgram(automateProg);
            glBindFramebuffer(GL_FRAMEBUFFER, fboA);
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, textureB);
            glUniform1i(AUTOMATE_TEXT, 0);
            glUniform1f(DU, 1.0/256);
            glUniform1f(DV, 1.0/256);
            // Update attribute values.
            glVertexAttribPointer(ATTRIB_VERTEX_2, 2, GL_FLOAT, 0, 0, squareVertices);
            glEnableVertexAttribArray(ATTRIB_VERTEX_2);

            glVertexAttribPointer(ATTRIB_TEXCOORD_2, 2, GL_FLOAT, GL_FALSE, 0, texCoord);    
            //glEnableVertexAttribArray(ATTRIB_TEXCOORD_2);
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
            if (![self validateProgram:automateProg]) {
                NSLog(@"Failed to validate program: %d", automateProg);
                return;
            }

            glBindFramebuffer(GL_FRAMEBUFFER, 0);
            glUseProgram(0);
        }
        else
        {
            glUseProgram(automateProg);            
            glBindFramebuffer(GL_FRAMEBUFFER, fboB);
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, textureA);
            glUniform1i(AUTOMATE_TEXT, 0);
            glUniform1f(DU, 1.0/256);
            glUniform1f(DV, 1.0/256);
            // Update attribute values.
            glVertexAttribPointer(ATTRIB_VERTEX_2, 2, GL_FLOAT, 0, 0, squareVertices);
            glEnableVertexAttribArray(ATTRIB_VERTEX_2);
            glVertexAttribPointer(ATTRIB_TEXCOORD_2, 2, GL_FLOAT, GL_FALSE, 0, texCoord); 
            //glEnableVertexAttribArray(ATTRIB_TEXCOORD_2);
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
            if (![self validateProgram:automateProg]) {
                NSLog(@"Failed to validate program: %d", automateProg);
                return;
            }

            glBindFramebuffer(GL_FRAMEBUFFER, 0);
            glUseProgram(0);
        }

        [(EAGLView *)self.view setFramebuffer];
        glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        if (counter % 2 == 0) {
            glUseProgram(normalProg);
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, textureB);
            glUniform1i(NORMAL_TEXT, 0);
            glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
            glEnableVertexAttribArray(ATTRIB_VERTEX);
            glVertexAttribPointer(ATTRIB_TEXCOORD, 2, GL_FLOAT, GL_FALSE, 0, texCoord); 
            glEnableVertexAttribArray(ATTRIB_TEXCOORD);
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
            if (![self validateProgram:normalProg]) {
                NSLog(@"Failed to validate program: %d", normalProg);
                return;
            }
            glUseProgram(0);

        } else {
            glUseProgram(normalProg);
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, textureA);
            glUniform1i(NORMAL_TEXT, 0);
            glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
            glEnableVertexAttribArray(ATTRIB_VERTEX);
            glVertexAttribPointer(ATTRIB_TEXCOORD, 2, GL_FLOAT, GL_FALSE, 0, texCoord); 
            glEnableVertexAttribArray(ATTRIB_TEXCOORD);
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
            if (![self validateProgram:normalProg]) {
                NSLog(@"Failed to validate program: %d", normalProg);
                return;
            }
            glUseProgram(0);
        }
        counter++;

[(EAGLView *)self.view presentFramebuffer];

片段着色器

precision mediump float;
varying vec2 v_texCoord;
uniform sampler2D tex; //the input texture
uniform float du; //the width of the cells
uniform float dv; //the height of the cells
    void main() {
        int count = 0;

        vec4 C = texture2D( tex, v_texCoord );
        vec4 E = texture2D( tex, vec2(v_texCoord.x + du, v_texCoord.y) );
        vec4 N = texture2D( tex, vec2(v_texCoord.x, v_texCoord.y + dv) );
        vec4 W = texture2D( tex, vec2(v_texCoord.x - du, v_texCoord.y) );
        vec4 S = texture2D( tex, vec2(v_texCoord.x, v_texCoord.y - dv) );
        vec4 NE = texture2D( tex, vec2(v_texCoord.x + du, v_texCoord.y + dv) );
        vec4 NW = texture2D( tex, vec2(v_texCoord.x - du, v_texCoord.y + dv) );
        vec4 SE = texture2D( tex, vec2(v_texCoord.x + du, v_texCoord.y - dv) );
        vec4 SW = texture2D( tex, vec2(v_texCoord.x - du, v_texCoord.y - dv) );

        if (E.r == 1.0) { count++; }
        if (N.r == 1.0) { count++; }
        if (W.r == 1.0) { count++; }
        if (S.r == 1.0) { count++; }
        if (NE.r == 1.0) { count++; }
        if (NW.r == 1.0) { count++; }
        if (SE.r == 1.0) { count++; }
        if (SW.r == 1.0) { count++; }

        if ( (count == 2 || count == 3)) {
            gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0); //cell lives...
        } else {
            gl_FragColor = vec4(0.0,0.0,0.0, 1.0); //cell dies...
        }
    }

Answer 1

我是否正确理解了您的代码，您想在第一个 if-else block 中将结果渲染到纹理，并在第二个 if-else 中将该结果渲染到屏幕- block ？如果是这样，那么看起来您在开始组织输入和输出的方式时犯了一个错误。这是您第一次通过时发生的情况(我减少了您的代码):

if(counter%2==0)
{
    glBindFramebuffer(GL_FRAMEBUFFER, fboA); // will render to textureA
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureB); // textureB is our input
} else {
    ...
}

if (counter % 2 == 0) {
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureB); // textureB still as input? not textureA?
} else {
    ...
}

...这是第二遍中发生的事情:

if(counter%2==0)
{
    ...
} else {
    glBindFramebuffer(GL_FRAMEBUFFER, fboB); // will render to textureB
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureA); // textureA as input
}

if (counter % 2 == 0) {
    ...
} else {
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureA); // textureA as input again?
}

您在第一帧中看到某些东西的原因是，您实际上渲染了您的输入数据，而不是第一次渲染的结果。而你第二遍出现黑屏的原因可能是你的片段着色器没有正常工作。从您的着色器代码来看，访问相邻纹素的错误似乎是最可能的原因。你能提供du和dv的值吗？

此外，正如 Brad 先前指出的那样，我认为仅使用一个纹理单元不会造成任何麻烦。不过我不确定。

旁注:对于乒乓你应该考虑创建你的 FBOs as an array使您的代码更具可读性。

编辑:

如果你在使用 glUniform1f() 设置制服 du 和 dv 时遇到问题，请尝试 glUniform1i() (然后您需要在着色器中使用 float() 进行转换)或 glUniform1fv() 代替。我曾经遇到过与 PowerVR GLES2 驱动程序相同的问题，该函数没有执行任何操作并导致制服为 0.0。