Compute Shader无法获取结果图像问题排查求助

我正在用Compute Shader筛选符合条件的颜色列，想把结果输出到1D图像imgOutput做后续处理，但没法通过get_img获取任何数据。下面是我的代码实现，麻烦帮忙排查问题（注：第一个代码块里的texture已经提前生成）：

C++ 代码实现 #

Shader spriteRowProgram, spriteColumnProgram;
unsigned int resultTexture = 0;
const std::string path = found::utils::Environment::GetRunPath();
const std::string sprite_row_path = path + "shaders/glfw_sprite_row.comp";
spriteRowProgram = Shader(sprite_row_path);
std::vector<GLfloat> get_img(qMax(TEX_WIDTH, TEX_HEIGHT) * 4);
glGenTextures(1, &resultTexture);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_1D, resultTexture);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA32F, qMax(TEX_WIDTH, TEX_HEIGHT), 0, GL_RGBA, GL_FLOAT, get_img.data());

glActiveTexture(GL_TEXTURE0 + 1);
glBindTexture(GL_TEXTURE_2D, texture);

spriteRowProgram.use();
glUniform1i(1, 1);
glBindImageTexture(1, texture, 0, GL_FALSE, 0, GL_READ_ONLY, GL_RGBA32F);
glUniform1i(0, 0);
glBindImageTexture(0, resultTexture, 0, GL_FALSE, 0, GL_WRITE_ONLY, GL_RGBA32F);
glClear(GL_COLOR_BUFFER_BIT);

spriteRowProgram.setInt("input_width", TEX_WIDTH);
spriteRowProgram.setInt("input_height", TEX_HEIGHT);
glDispatchCompute(TEX_WIDTH, 1, 1);
glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);

Compute Shader 代码实现 #

#version 430 core
layout (local_size_x = 1, local_size_y = 1) in;
layout(rgba32f, location = 0, binding = 0) uniform writeonly image1D imgOutput;

// texture samplers
layout(rgba32f, location = 1, binding = 1) uniform readonly image2D inputImage;
uniform int input_width;
uniform int input_height;

void main()
{
    vec4 baseColor = imageLoad(inputImage, ivec2(0, 0));
    bool alpha = baseColor.w == 1;
    bool success = true;
    for (int i = 0; i <= input_height; ++i)
    {
        vec4 current = imageLoad(inputImage, ivec2(gl_GlobalInvocationID.x, i));
        if (alpha) {
            if (current.w > 0.99) continue;
            else {
                success = false;
                break;
            }
        } else {
            vec4 difference = baseColor - current;
            success = abs(difference.x) < 0.01 && abs(difference.y) < 0.01 && abs(difference.z) < 0.01;
            if (success) continue;
            else {
                break;
            }
        }
    }
    if (success) baseColor = ivec4(0.1, 0.1, 0.1, 0.1);
    else baseColor = ivec4(1.0, 1.0, 1.0, 1.0);
    imageStore(imgOutput, int(gl_GlobalInvocationID.x), baseColor);
}

问题排查与修复方案 #

• 缺少GPU到CPU的数据读取步骤：你仅用get_img初始化了纹理，但Compute Shader执行后，没有将GPU上的resultTexture数据读回CPU。在glMemoryBarrier后添加以下代码：

  glBindTexture(GL_TEXTURE_1D, resultTexture);
  glGetTexImage(GL_TEXTURE_1D, 0, GL_RGBA, GL_FLOAT, get_img.data());
  

• 1D纹理参数设置错误：1D纹理只有S轴，GL_TEXTURE_WRAP_T参数无效，删除该行：

  // glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
  

• Shader中纹理访问越界：循环条件i <= input_height会访问超出图像范围的像素（图像y坐标范围是0到input_height-1），修改为：

  for (int i = 0; i < input_height; ++i)
  

• 类型转换错误：将ivec4赋值给vec4会导致浮点数值被截断，改用vec4直接赋值：

  if (success) baseColor = vec4(0.1, 0.1, 0.1, 0.1);
  else baseColor = vec4(1.0, 1.0, 1.0, 1.0);
  

• 冗余的Uniform设置：image类型的资源通过binding布局直接绑定，不需要用glUniform1i设置纹理单元，删除以下两行：

  // glUniform1i(1, 1);
  // glUniform1i(0, 0);
  

• 内存屏障类型不匹配：写入图像纹理后，应使用GL_TEXTURE_FETCH_BARRIER_BIT确保数据可见性，修改内存屏障：

  glMemoryBarrier(GL_TEXTURE_FETCH_BARRIER_BIT);
  

内容的提问来源于stack exchange，提问作者0ices