How to cover the PNG image with another PNG image?

[lifecat9]

My Code :

Code: Select all

#include <sdl.h>
#include <sdl_image.h>

void main&#40;&#41;&#123;
  Surf_Display = SDL_SetVideoMode&#40;400,400, 32, SDL_HWSURFACE | SDL_DOUBLEBUF&#41;&#41;;
  SDL_Surface* png1 = IMG_Load&#40;"png1.png"&#41;;
  SDL_Surface* png2 = IMG_Load&#40;"png2.png"&#41;;
  SDL_BlitSurface&#40;png1, NULL, png2,NULL&#41;;
  SDL_BlitSurface&#40;png2, NULL,Surf_Display,NULL&#41;;
  SDL_Flip&#40;Surf_Display&#41;;
  
&#125;

[ne0h]

You are blitting your image in the pn2 surface!

Code: Select all

#include <sdl.h>
#include <sdl_image.h>

void main&#40;&#41;&#123;
  Surf_Display = SDL_SetVideoMode&#40;400,400, 32, SDL_HWSURFACE | SDL_DOUBLEBUF&#41;&#41;;
  SDL_Surface* png1 = IMG_Load&#40;"png1.png"&#41;;
  SDL_Surface* png2 = IMG_Load&#40;"png2.png"&#41;;
  SDL_BlitSurface&#40;png2, NULL,Surf_Display,NULL&#41;;
  SDL_BlitSurface&#40;png1, NULL, Surf_Display,NULL&#41;;
  SDL_Flip&#40;Surf_Display&#41;;
 
&#125;

Try this...

[lifecat9]

You are blitting your image in the pn2 surface!

Code: Select all

#include <sdl.h>
#include <sdl_image.h>

void main&#40;&#41;&#123;
  Surf_Display = SDL_SetVideoMode&#40;400,400, 32, SDL_HWSURFACE | SDL_DOUBLEBUF&#41;&#41;;
  SDL_Surface* png1 = IMG_Load&#40;"png1.png"&#41;;
  SDL_Surface* png2 = IMG_Load&#40;"png2.png"&#41;;
  SDL_BlitSurface&#40;png2, NULL,Surf_Display,NULL&#41;;
  SDL_BlitSurface&#40;png1, NULL, Surf_Display,NULL&#41;;
  SDL_Flip&#40;Surf_Display&#41;;
 
&#125;

Try this...

That's a good idea,think you!

But the Surf_Display will lost png1 and png2's alpha informats(suppose Surf_Display is transparence).How to save alpha informats?

[Raphael]

Short answer: you simply can't on PSP

[lifecat9]

Short answer: you simply can't on PSP

?????
Yes!I cross out some codes;

this is SDL problem,of course you can use SDL in PSP.

[Raphael]

OK, a little longer answer to make it clear:
You can't write to alpha on PSP (hardware limitation unless SDL would use a software method for blended blitting which is just slow), hence why you can't save the alpha part of png1 into png2 and then blit that to screen.
You have to do as ne0h suggested and just blit your images to screen directly in the proper order.