/// <summary>
/// Allows to swap render target in a simple manner.
/// Note that the returned object is disposable and on calling Dispose the original rendertarget binding is restored.
/// Recommend way of usage: using statement (all rendering within the using block).
/// </summary>
/// <param name="renderContext"></param>
/// <param name="renderTarget">The rendertarget to write to. Use null if you want to render to the actuall backbuffer.</param>
/// <param name="usage"></param>
/// <returns></returns>
public static IDisposable RenderTo(this IRenderContext renderContext, RenderTarget2D renderTarget, BackBufferSwapUsage usage = BackBufferSwapUsage.WpfSupport)
{
return(new RenderTargetHelper(renderContext, renderTarget, usage));
}
/// <summary>
/// When invoked will insert the renderTargets as the currently active one and save itself a reference back to the original one.
/// On <see cref="Dispose"/> the rendertarget is detached and the original one is swapped back in.
/// </summary>
/// <param name="renderContext"></param>
/// <param name="renderTarget">The rendertarget to be used.</param>
/// <param name="usage"></param>
public RenderTargetHelper(IRenderContext renderContext, RenderTarget2D renderTarget, BackBufferSwapUsage usage)
{
_renderContext = renderContext;
// check if there is an existing rendertarget bound to the graphicsdevice
// there are 4 possible options. existing rendertarget and target rendertarget can both be null or some rendertarget so we need to check which state it is for us
// the 4 options: null & null, null & rt, rt & null, rt & rt
_originalRenderTarget = renderContext.GraphicsDevice.RenderTargetCount > 0
? renderContext.GraphicsDevice.GetRenderTargets()[0]
: (RenderTargetBinding?)null;
// user requested backbuffer when he only provided one RT which he set to null
var backBufferRequested = renderTarget == null;
if (backBufferRequested)
{
if (_originalRenderTarget == null)
{
// 1. option, rendertarget is null and user wants to draw to backbuffer -> no need for swapping
_resetToBackBuffer = true;
return;
}
// 3. option: user wants to draw to the back buffer, but a rendertarget already exists
// user wants to render directly to backbuffer, however someone has already set a rendertarget
// this is the case e.g. for the WPF interop: https://github.com/MarcStan/MonoGame.Framework.WpfInterop
// which doesn't write to the normal backbuffer but writes to a 3D11 image host instead (which in turn can be displayed in WPF)
// so we can't actually render to backbuffer as it won't be visible then
// instead user selected WpfSupport, so don't set to null but keep the rendertarget that is set
_resetToBackBuffer = usage != BackBufferSwapUsage.WpfSupport;
}
else
{
// 2. and 4. option
// we set a rendertarget and then later reset to the original rendertarget (which is either null or an existing one)
_resetToBackBuffer = true;
}
// only set the target rt if we are actually going to swap back to source
// otherwise source = target
if (_resetToBackBuffer)
{
renderContext.GraphicsDevice.SetRenderTarget(renderTarget);
}
}
