Question

我写了一个简单的测试用例来获取计算着色器中图像的高度并将其写入SSBO。我已经使用了SSBO代码before，我知道这部分工作正常。我在glDispatchCompute调用期间使用apitrace检查状态，我可以看到原始纹理和绑定到正确图像单元的图像。但是，imageSize总是返回零（输出全部为零，但最后一些剩余的-1s除外，因为工作组大小的除法向下舍入）。不会抛出OpenGL错误。

我将此测试用例基于我之前的一个问题，其中包括将SSBO绑定到计算着色器的代码（我在此处使用它来从计算着色器获取调试输出）。

class ComputeShaderWindow : public QOpenGLWindow {
  public:
    void initializeGL() {
        // Create the opengl functions object
        gl = context()->versionFunctions<QOpenGLFunctions_4_3_Core>();
        m_compute_program = new QOpenGLShaderProgram(this);
        auto compute_shader_s = fs::readFile(
                                    "test_assets/example_compute_shader.comp");
        QImage img("test_assets/input/out.png");
        // Adds the compute shader, then links and binds it
        m_compute_program->addShaderFromSourceCode(QOpenGLShader::Compute,
                compute_shader_s);
        m_compute_program->link();
        m_compute_program->bind();

        GLuint frame;

        // Create the texture
        gl->glGenTextures(1, &frame);

        // Bind the texture
        gl->glBindTexture(GL_TEXTURE_2D, frame);

        // Fill the texture with the image
        gl->glTexImage2D(GL_TEXTURE_2D,
                         0,
                         GL_RGB8,
                         img.width(),
                         img.height(),
                         0,
                         GL_BGRA,
                         GL_UNSIGNED_BYTE,
                         img.bits());
        GLuint image_unit = 1;
        // Get the location of the image uniform
        GLuint uniform_location = gl->glGetUniformLocation(
                                      m_compute_program->programId(),
                                      "video_frame");
        // Set location to 0 (a unique value that we choose)
        gl->glUniform1i(uniform_location, image_unit);
        // Bind layer of texture to image unit
        gl->glBindImageTexture(image_unit,
                               frame,
                               0,
                               GL_FALSE,
                               0,
                               GL_READ_ONLY,
                               GL_RGBA8UI);
        // We should only need the bit for shader image access,
        // but for the purpose of this example, I set all the bits
        // just to be safe
        gl->glMemoryBarrier(GL_ALL_BARRIER_BITS);

        // SSBO stuff to get output from the shader
        GLfloat* default_values = new GLfloat[NUM_INVOCATIONS];
        std::fill(default_values, default_values + NUM_INVOCATIONS, -1.0);
        GLuint ssbo;
        gl->glGenBuffers(1, &ssbo);
        gl->glBindBuffer(GL_SHADER_STORAGE_BUFFER, ssbo);
        gl->glBufferData(GL_SHADER_STORAGE_BUFFER,
                         NUM_INVOCATIONS * sizeof(float),
                         &default_values[0],
                         GL_STATIC_DRAW);
        gl->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, ssbo);
        gl->glDispatchCompute(NUM_INVOCATIONS / WORKGROUP_SIZE, 1, 1);
        gl->glMemoryBarrier(GL_VERTEX_ATTRIB_ARRAY_BARRIER_BIT);
        gl->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, ssbo);

        // Now read from the buffer so that we can check its values
        GLfloat* read_data = (GLfloat*) gl->glMapBuffer(GL_SHADER_STORAGE_BUFFER,
                             GL_READ_ONLY);
        std::vector<GLfloat> buffer_data(NUM_INVOCATIONS);

        // Read from buffer
        for (int i = 0; i < NUM_INVOCATIONS; i++) {
            DEBUG(read_data[i]);
        }
        DEBUG("Done!");

        gl->glUnmapBuffer(GL_SHADER_STORAGE_BUFFER);
        assert(gl->glGetError() == GL_NO_ERROR);
    }

    void resizeGL(int width, int height) {

    }

    void paintGL() {

    }

    void teardownGL() {

    }

  private:
    QOpenGLFunctions_4_3_Core* gl;
    QOpenGLShaderProgram* m_compute_program;
    static constexpr int NUM_INVOCATIONS = 9000;
    static constexpr int WORKGROUP_SIZE = 128;
};

对于计算着色器：

#version 430 core

layout(local_size_x = 128) in;

layout(rgba8ui, binding = 1) readonly uniform uimage2D video_frame;

layout(std430, binding = 0) writeonly buffer SSBO {
    float data[];
};

void main() {
    uint ident = int(gl_GlobalInvocationID);
    uint num_workgroups = int(gl_WorkGroupID);
    // Write the height of the image into the buffer
    data[ident] = float(imageSize(video_frame).y);
}

Answer 1

原来我忘记了纹理参数：

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

不知道为什么会打破imageSize()来电。

OpenGL imageSize始终为零

1 个答案: