# GLViewer CUDA-OpenGL Interop Fix

## Problem

The GLViewer had CUDA-OpenGL interop issues where the application would crash or display corrupted graphics when rendering point clouds and camera views. This was caused by improper resource mapping between CUDA and OpenGL.

## Root Cause

The original code kept CUDA graphics resources permanently mapped:
- Resources were mapped once during initialization
- Never unmapped until cleanup/resize
- CUDA and OpenGL were competing for the same memory resources

This violates CUDA-OpenGL interop best practices which require:
1. **Map** resource before CUDA operations
2. **Use** the mapped pointer/array
3. **Unmap** resource before OpenGL uses it

## Solution Applied

### 1. PointCloud::pushNewPC() Fix

**Before:**
```cpp
void PointCloud::pushNewPC() {
    // ... initialization code ...
    // Resource mapped once, never unmapped
    cudaMemcpy(xyzrgbaMappedBuf_, refMat.getPtr<sl::float4>(sl::MEM::CPU), 
               numBytes_, cudaMemcpyHostToDevice);
}
```

**After:**
```cpp
void PointCloud::pushNewPC() {
    // ... initialization code ...
    
    // Map the resource for CUDA access
    cudaError_t err = cudaGraphicsMapResources(1, &bufferCudaID_, 0);
    
    err = cudaGraphicsResourceGetMappedPointer((void**)&xyzrgbaMappedBuf_, 
                                               &numBytes_, bufferCudaID_);
    
    // Copy data from ZED SDK to mapped OpenGL buffer
    cudaMemcpy(xyzrgbaMappedBuf_, refMat.getPtr<sl::float4>(sl::MEM::CPU), 
               numBytes_, cudaMemcpyHostToDevice);
    
    // Synchronize to ensure copy completes
    cudaStreamSynchronize(0);
    
    // Unmap so OpenGL can use it
    err = cudaGraphicsUnmapResources(1, &bufferCudaID_, 0);
}
```

### 2. CameraViewer::pushNewImage() Fix

**Before:**
```cpp
void CameraViewer::pushNewImage() {
    if (!ref.isInit())  return;
    // ArrIm was permanently mapped, direct copy
    cudaMemcpy2DToArray(ArrIm, 0, 0, ref.getPtr<sl::uchar1>(sl::MEM::CPU), 
                        ref.getStepBytes(sl::MEM::CPU), 
                        ref.getPixelBytes() * ref.getWidth(), 
                        ref.getHeight(), cudaMemcpyHostToDevice);
}
```

**After:**
```cpp
void CameraViewer::pushNewImage() {
    if (!ref.isInit())  return;

    // Map the resource for CUDA access
    auto err = cudaGraphicsMapResources(1, &cuda_gl_ressource, 0);

    err = cudaGraphicsSubResourceGetMappedArray(&ArrIm, cuda_gl_ressource, 0, 0);

    // Copy data to mapped array
    err = cudaMemcpy2DToArray(ArrIm, 0, 0, ref.getPtr<sl::uchar1>(sl::MEM::CPU), 
                              ref.getStepBytes(sl::MEM::CPU), 
                              ref.getPixelBytes() * ref.getWidth(), 
                              ref.getHeight(), cudaMemcpyHostToDevice);

    // Synchronize to ensure copy completes
    cudaStreamSynchronize(0);

    // Unmap so OpenGL can use it
    err = cudaGraphicsUnmapResources(1, &cuda_gl_ressource, 0);
}
```

### 3. CameraViewer Initialization Cleanup

Removed permanent mapping from initialization:

**Before:**
```cpp
// In CameraViewer::initialize():
cudaGraphicsGLRegisterImage(&cuda_gl_ressource, texture, GL_TEXTURE_2D, 
                            cudaGraphicsRegisterFlagsWriteDiscard);
cudaGraphicsMapResources(1, &cuda_gl_ressource, 0);  // REMOVED
cudaGraphicsSubResourceGetMappedArray(&ArrIm, cuda_gl_ressource, 0, 0);  // REMOVED
```

**After:**
```cpp
// In CameraViewer::initialize():
cudaGraphicsGLRegisterImage(&cuda_gl_ressource, texture, GL_TEXTURE_2D, 
                            cudaGraphicsRegisterFlagsWriteDiscard);
// Mapping now done in pushNewImage()
```

## Key CUDA-OpenGL Interop Rules

1. **Register once** - `cudaGraphicsGLRegisterBuffer/RegisterImage`
2. **Map before CUDA** - `cudaGraphicsMapResources`
3. **Get pointer/array** - `cudaGraphicsResourceGetMappedPointer/SubResourceGetMappedArray`
4. **Copy data** - `cudaMemcpy/cudaMemcpy2DToArray`
5. **Synchronize** - `cudaStreamSynchronize` (ensures copy completes)
6. **Unmap before GL** - `cudaGraphicsUnmapResources`
7. **Unregister on cleanup** - `cudaGraphicsUnregisterResource`

## Reference

This fix is based on commit `45fcb88e9dcc7a1b1fb86b928b884bfcdc1da0f2` in the zed-sdk repository which applied the same fix to the depth sensing sample.