Function ReadbackPixels

source/graphics_platform_d3d11.cpp:188–249

// ***********************************************************************

void ReadbackPixels(int x, int y, int w, int h, void *pixels) {
    // get current render target
    ID3D11RenderTargetView* render_target_view = NULL;
	_sg.d3d11.ctx->OMGetRenderTargets(1, &render_target_view, NULL);

    // fallback to window render target
    if(!render_target_view)
        render_target_view = (ID3D11RenderTargetView*)_sg.d3d11.cur_pass.render_view;

	if (render_target_view == nullptr)
		return;

    // get the back buffer texture
    ID3D11Texture2D *back_buffer = NULL;
	render_target_view->GetResource((ID3D11Resource**)&back_buffer);

    // create a staging texture to copy the screen's data to
    D3D11_TEXTURE2D_DESC staging_desc;
	back_buffer->GetDesc(&staging_desc);
    staging_desc.Width = w;
    staging_desc.Height = h;
    staging_desc.BindFlags = 0;
    staging_desc.MiscFlags = 0;
    staging_desc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
    staging_desc.Usage = D3D11_USAGE_STAGING;
    ID3D11Texture2D *staging_tex = NULL;
    _sg_d3d11_CreateTexture2D(_sg.d3d11.dev, &staging_desc, NULL, &staging_tex);

    // copy the desired portion of the back buffer to the staging texture
    D3D11_BOX src_box = {
        .left = (UINT)x,
        .top = (UINT)y,
        .front = 0,
        .right = (UINT)(x + w),
        .bottom = (UINT)(y + h),
        .back = 1,
    };
	_sg.d3d11.ctx->CopySubresourceRegion(
		(ID3D11Resource*)staging_tex,
        0, 0, 0, 0,
        (ID3D11Resource*)back_buffer,
        0, &src_box);

    // map the staging texture's data to CPU-accessible memory
    D3D11_MAPPED_SUBRESOURCE msr = {.pData = NULL};
    _sg_d3d11_Map(_sg.d3d11.ctx, (ID3D11Resource*)staging_tex, 0, D3D11_MAP_READ, 0, &msr);

    // copy the data into the desired buffer, converting pixels to the desired format at the same time
    int res = SDL_ConvertPixels(
        w, h,
        _sg_d3d11_dxgi_format_to_sdl_pixel_format(staging_desc.Format),
        msr.pData, msr.RowPitch,
        SDL_PIXELFORMAT_RGBA32,
        pixels, w * 4);
    _SOKOL_UNUSED(res);

    // unmap the texture
    _sg_d3d11_Unmap(_sg.d3d11.ctx, (ID3D11Resource*)staging_tex, 0);