I just stumbled upon some typing issues.
1. The ratio parameter in the PostProcess contructor is defined as "number | any" but in all derived classes (FxaaPostProcess ...) it is define as "number" only. see:
https://github.com/BabylonJS/Babylon.js/blob/master/src/PostProcess/babylon.postProcess.ts#L100
https://github.com/BabylonJS/Babylon.js/blob/master/src/PostProcess/babylon.fxaaPostProcess.ts#L6
2. There are some issues with the size parameter of the RenderTargetTexture:
- in the constructor its defined as "any" but it should be "number | any"
- the private member "_size" is defined as "number" but should be "number | any"
- the getRenderSize() function returns "number" but should return "number | any"
- the scale() function expects "_size" to be "number" and will fail if it is an object:
https://github.com/BabylonJS/Babylon.js/blob/master/src/Materials/Textures/babylon.renderTargetTexture.ts#L168