cuda地形遮蔽代码

CUDA地形遮蔽是指使用CUDA在GPU上实现的地形遮蔽算法，它可以实现在渲染地形时，根据地形高度信息和光照信息，将地形上的阴影部分加深，以达到更加逼真的效果。

实现CUDA地形遮蔽的基本步骤如下：
1. 将地形高度数据和光照信息加载到GPU显存中；
2. 使用CUDA内核函数进行并行计算，计算每个像素点是否受到阴影的遮挡；
3. 将计算结果写回到显存中；
4. 将结果传回CPU，进行后续渲染处理。

下面是一个简单的CUDA地形遮蔽代码示例：

__global__ void terrain_shading_kernel(float* height_map, float* light_map, float* shadow_map, int width, int height)
{
    int i = blockIdx.x * blockDim.x + threadIdx.x;
    int j = blockIdx.y * blockDim.y + threadIdx.y;
    
    if (i >= width || j >= height) return;
    
    float height = height_map[i * width + j];
    float light = light_map[i * width + j];
    float shadow = 0.0f;
    
    for (int k = 0; k < NUM_SAMPLES; k++) {
        float h = height_map[(i + SAMPLES[k].x) * width + (j + SAMPLES[k].y)];
        float l = light_map[(i + SAMPLES[k].x) * width + (j + SAMPLES[k].y)];
        if (h < height) {
            shadow += (height - h) / (height - MIN_HEIGHT) * l;
        }
    }
    
    shadow /= (float)NUM_SAMPLES;
    shadow_map[i * width + j] = shadow;
}

int main()
{
    // Load height map and light map into GPU memory
    float* d_height_map;
    float* d_light_map;
    cudaMalloc(&d_height_map, width * height * sizeof(float));
    cudaMalloc(&d_light_map, width * height * sizeof(float));
    cudaMemcpy(d_height_map, height_map, width * height * sizeof(float), cudaMemcpyHostToDevice);
    cudaMemcpy(d_light_map, light_map, width * height * sizeof(float), cudaMemcpyHostToDevice);
    
    // Allocate memory for shadow map on GPU
    float* d_shadow_map;
    cudaMalloc(&d_shadow_map, width * height * sizeof(float));
    
    // Launch kernel to compute terrain shading
    dim3 block_size(16, 16);
    dim3 grid_size((width + block_size.x - 1) / block_size.x, (height + block_size.y - 1) / block_size.y);
    terrain_shading_kernel<<<grid_size, block_size>>>(d_height_map, d_light_map, d_shadow_map, width, height);
    
    // Copy shadow map back to CPU memory and free GPU memory
    cudaMemcpy(shadow_map, d_shadow_map, width * height * sizeof(float), cudaMemcpyDeviceToHost);
    cudaFree(d_height_map);
    cudaFree(d_light_map);
    cudaFree(d_shadow_map);
    
    return 0;
}