Question

我的C ++代码是专为iOS而设计的，现在我将其移植到NDK并进行了少量修改。

我绑定帧缓冲区并调用

glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

然后我像这样绑定主帧缓冲区

glBindFramebuffer(GL_FRAMEBUFFER, 0);

glGetError()返回GL_INVALID_FRAMEBUFFER_OPERATION

我可以在我的帧缓冲区中绘制并使用其纹理在主帧缓冲区中绘制它。但是当我打电话给glReadPixels然后我得到零

该代码在iOS中有效，而且除了glReadPixels

外，大部分内容都适用于Android

glCheckFramebufferStatus(GL_FRAMEBUFFER)返回GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT 0x8CD7

-

我会考虑一些示例代码，它会为我提供来自帧缓冲区或纹理的像素数据，我可以将其保存为文件answer

现在我可以使用附加纹理绘制到缓冲区，我可以使用该纹理在主缓冲区上绘制。但我无法从帧缓冲区/纹理中获取像素以保存到文件或发布到Facebook。

Answer 1

我已经能够从帧缓冲区执行glReadPixels修改NDK示例“GL2JNIActivity”。

我刚刚更改了gl_code.cpp，我添加了一个初始化函数：

char *pixel = NULL;
GLuint fbuffer, rbuffers[2];
int width, height;
bool setupMyStuff(int w, int h) {
     // Allocate the memory
     if(pixel != NULL) free(pixel);
     pixel = (char *) calloc(w * h * 4, sizeof(char)); //4 components
     if(pixel == NULL)  {
                  LOGE("memory not allocated!");
                       return false;
                       }

                       // Create and bind the framebuffer
    glGenFramebuffers(1, &fbuffer);
    checkGlError("glGenFramebuffer");

    glBindFramebuffer(GL_FRAMEBUFFER, fbuffer);
    checkGlError("glBindFramebuffer");

    glGenRenderbuffers(2, rbuffers);
    checkGlError("glGenRenderbuffers");

    glBindRenderbuffer(GL_RENDERBUFFER, rbuffers[0]);
    checkGlError("glGenFramebuffer[color]");

    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGB565, w, h);
    checkGlError("glGenFramebuffer[color]");

    glBindRenderbuffer(GL_RENDERBUFFER, rbuffers[1]);
    checkGlError("glGenFramebuffer[depth]");

    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, w, h);
    checkGlError("glGenFramebuffer[depth]");

    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rbuffers[0]);
    checkGlError("glGenFramebuffer[color]");
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,  GL_RENDERBUFFER, rbuffers[1]);
    checkGlError("glGenFramebuffer[depth]");

    if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
                                                    LOGE("Framebuffer not complete");
                                                    return false;
    }

    // Turn this on to confront the results in pixels when the fb is active with the ones obtained from the screen
    if(false) {
                  glBindFramebuffer(GL_FRAMEBUFFER, 0);
        checkGlError("glBindFramebuffer");
    }

    width = w;
    height = h;

    return true;
}

除了初始化帧缓冲区并为输出分配空间之外什么也没做，我在

的最后调用它

bool setupGraphics(int w, int h);

和一个块来保存像素数组中的输出（我明显地在

之后执行

    checkGlError("glDrawArrays");

renderFrame（）中的

语句：

{ 
// save the output of glReadPixels somewhere... I'm a noob about JNI however, so I leave this part as an exercise for the reader ;-)
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixel);
checkGlError("glReadPixel(0, 0, w, h, GL_RGB, GL_UNSIGNED_BYTE, pixel)");
int end = width * height * 4 - 1;
// This function returns the same results regardless of where the data comes from (screen or fbo)
LOGI("glReadPixel => (%hhu,%hhu,%hhu,%hhu),(%hhu,%hhu,%hhu,%hhu),(%hhu,%hhu,%hhu,%hhu),..., (%hhu, %hhu, %hhu, %hhu)",
      pixel[0], pixel[1], pixel[2], pixel[3],
      pixel[4], pixel[5], pixel[6], pixel[7],
      pixel[8], pixel[9], pixel[10], pixel[11],
      pixel[end - 3], pixel[end - 2], pixel[end - 1], pixel[end]);
}

无论是在帧缓冲区还是在屏幕上绘制，logcat中的结果都是相同的：

I/libgl2jni( 5246): glReadPixel => (0,4,0,255),(8,4,8,255),(0,4,0,255),..., (0, 4, 0, 255)
I/libgl2jni( 5246): glReadPixel => (8,4,8,255),(8,8,8,255),(0,4,0,255),..., (8, 8, 8, 255)
I/libgl2jni( 5246): glReadPixel => (8,8,8,255),(8,12,8,255),(8,8,8,255),..., (8, 8, 8, 255)
I/libgl2jni( 5246): glReadPixel => (8,12,8,255),(16,12,16,255),(8,12,8,255),..., (8, 12, 8, 255)
I/libgl2jni( 5246): glReadPixel => (16,12,16,255),(16,16,16,255),(8,12,8,255),..., (16, 16, 16, 255)
[...]

在Froyo（手机）和4.0.3平板电脑上进行了测试。

您可以在原始NDK示例（GL2JNIActivity）中找到所有其他详细信息。

希望这有帮助

编辑：也请务必核对：

Android NDK glReadPixels() from offscreen buffer

海报似乎有相同的症状（并解决了从正确的线程调用glReadPixels的问题）。

GL_INVALID_FRAMEBUFFER_OPERATION Android NDK GL FrameBuffer和glReadPixels返回0 0 0 0

1 个答案: