第一帧后，两个FBO之间的乒乓渲染失败. [英] Ping-pong rendering between two FBOs fails after first frame.
问题描述
我正在尝试创建两个FBO并实现乒乓渲染.但是，我只有第一帧才能正常工作.我正在尝试模拟人生游戏，在第一帧之后，我只会得到黑屏.你能帮我检查一下吗?我在这个问题上花了几个小时.
I am trying to create two FBOs and implement a ping-pong render. But, I only get the first frame to work properly. I am trying to simulate a game-of-life and, after the first frame, I only get a black screen. Could you help me check it? I have spent hours on this issue.
修改
也许我没有描述清楚.实际上，我想将textureB用作纹理并将其渲染到textureA，然后使用textureA渲染到屏幕，反之亦然.
Maybe I didn't describe clearly. Actually, I want to use the textureB as the texture and render it to textureA, then use the textureA to render to screen, then vice versa.
修改 我可以看到第一帧，即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还原为白色，将白色还原为黑色.它仍然变成全黑.
Edit I can see the first frame, which is the textureB. After it go through the fragment shader, it become black. At first, I suspect the fragment shader, I change it to only revert the black to white and white to black. It still becomes all black.
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...
}
}
推荐答案
我理解您的代码正确吗，您想将结果渲染到第一个if-else块中的纹理并将结果渲染到屏幕中.第二个if-else块?
如果是这样，那么看来您在如何组织输入和输出时就犯了一个错误.
这是您的第一遍操作(我减少了代码):
Do I understand your code right, that you want to render a result to a texture in the first if-else-block and render that result to screen in the second if-else-block?
If so, then it looks like you have a mistake in how you organize your input and output to begin with.
This is what happens in your first pass (I reduced your code):
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 {
...
}
...这就是第二遍:
...and this is what happens in the second pass:
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?
}
之所以在第一帧中看到某些内容，是因为您实际上是在渲染输入数据，而不是第一次通过的结果.并且第二遍中出现黑屏的原因可能是您的片段着色器无法正常工作.从您的着色器代码来看，访问邻近纹理像素的错误似乎是最可能的原因.您可以提供du和dv的值吗?
The reason why you see something in the first frame is, because you actually render your input data, but not the result of your first pass. And the reason why you have black screen in your second pass may be that your fragment shader does not work correctly. Judging from your shader code, a mistake in accessing the neighbor texels seems to be the most plausible cause for that. Can you provide the values of duand dv?
而且，正如布拉德(Brad)先前指出的那样，我也不认为仅使用一个纹理单元会造成任何麻烦.不过我不确定.
Also I don't think that using only one texture unit should make any trouble, as Brad pointed out earlier. I'm not sure about that though.
On a side note: for ping-ponging you should consider creating your FBOs as an array to make your code a lot more readable.
我在用glUniform1f()设置制服du和dv时遇到问题，请尝试glUniform1i()(然后需要在着色器中使用float()进行投射)或glUniform1fv().我曾经在PowerVR GLES2驱动程序中遇到过相同的问题，其中该功能没有执行任何操作，导致统一的文件为0.0.
I you have problems setting your uniforms du and dv with glUniform1f(), try glUniform1i() (you need to cast with float() in your shader then) or glUniform1fv() instead. I once had the same problem with the PowerVR GLES2 drivers, where this function didn't do anything and caused the uniform to be 0.0.
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