SDL_RenderCopy() has strange behavior on Raspberry PI

Question

This is driving me up the wall..
I've got a very simple SDL2 program.
It has a array of 3 SDL_Texture pointers.
These textures are filled as follows:

SDL_Texture *myarray[15];
SDL_Surface *surface;

for(int i=0;i<3;i++)
{
   char filename[] = "X.bmp";
   filename[0] = i + '0';
   surface = SDL_LoadBMP(filename);
   myarray[i] = SDL_CreateTextureFromSurface(myrenderer,surface);
   SDL_FreeSurface(surface);
}

This works, no errors.

In the main loop (which is just a standard event loop waiting for SDL_QUIT, keystrokes and a user-event which a SDL_Timer puts in the event queue every second) I just do (for the timer triggered event):

idx = (idx+1) % 3;         // idx is global var initially 0.
SDL_RenderClear(myrenderer);
SDL_RenderCopy(myrenderer,  myarray[idx], NULL, NULL);
SDL_RendererPresent(myrenderer);

This works fine for 0.bmp and 1.bmp, but the 3rd image (2.bmp) simply shows as a black field.
This is structural.
If I alternate the first 2 images they are both fine.
If I alternate the 2nd and 3rd image the 3rd image doesn't show.
If I use more than 3 images then 3 and upwards show as black.
Loading order doesn't matter. It starts going wrong with the 3rd image loaded from disk.
All images are properly formatted BMP's. I even saved 2.bmp back to disk under a different name by using SDL_SaveBMP() after it was loaded to make sure it got loaded in memory OK. The new file is bit for bit identical to the original.

This program, without modifications and the same bmp files, works fine on OSX (XCode5) and Windows (VC++ 2012 Express).
The problem only shows on the Raspberry PI.
I have placed explicit error checks on every call that can leave a result/error-code (not shown in the samples above for brevity) but all of them show "no error".
I have used the latest stable source set of www.libsdl.org and compiled as instructed (configure, make, make install, etc.).

Anybody got any idea what could be going on ?

PS Keyboard input doesn't seem to work either on my PI, but I haven't delved into that yet.

Answer 1

Answering myself as I finally figured it out myself...

I finally went back to the README-raspberrypi.txt that came with the SDL2 sources.
I didn't read it carefully enough the first time around...

Problem 1: I'am running on a FULL-HD display. The PI's default GPU memory is 64MB which is not enough for large displays and double-buffering. As suggested in the README I increased this to 128MB and this solved the black image problem.

Problem 2: Text input wasn't working because my user-account was not in the input group. I had added the default "pi" account to the input group initially, but when I later started using another account I forgot to add that user to the group.

In short: Caught by my own (too) quick skimming of the documentation.