I'm working on a Space Invaders emulator and for display output I'm using SDL2.
The problem is that on the output window I see all the frames since emulation starts!
Basically the important piece of code is this:
Intel8080 mainObject; // My Intel 8080 CPU emulator
mainObject.loadROM();
//Main loop flag
bool quit = false;
//Event handler
SDL_Event e;
//While application is running
while (!quit)
{
//Handle events on queue
while (SDL_PollEvent(&e) != 0)
{
//User requests quit
if (e.type == SDL_QUIT)
{
quit = true;
}
}
if (mainObject.frameReady)
{
mainObject.frameReady = false;
gHelloWorld = SDL_CreateRGBSurfaceFrom(&mainObject.frameBuffer32, 256, 224, 32, 4 * 256, 0xff000000, 0x00ff0000, 0x0000ff00, 0x000000ff);
//Apply the image
SDL_BlitSurface(gHelloWorld, NULL, gScreenSurface, NULL);
//Update the surface
SDL_UpdateWindowSurface(gWindow);
}
mainObject.executeROM();
}
where Intel8080 is my CPU emulator code and mainObject.frameBuffer32 is the Space Invaders' video RAM that I converted from 1bpp to 32bpp in order to use SDL_CreateRGBSurfaceFrom function.
Emulation's working fine but I see all the frames generated since emulator starts!
I tried to change Alpha value in the 4 bytes of each RGBA pixel but nothing changes
This is happening because it looks like you're rendering the game without first clearing the window. Basically, you should fill the entire window with a color and then render on top of it constantly. The idea is that filling the window with a specific color before rendering over it is the equivalent of erasing the previous frame (most modern computers are powerful enough to handle this).
You might want to read-up on SDL's SDL_FillRect function, it'll allow you to fill the entire screen with a specific color.
Rendering pseudocode:
while(someCondition)
{
[...]
// Note, I'm not sure if "gScreenSurface" is the proper variable to use here.
// I got it from reading your code.
SDL_FillRect(gScreenSurface, NULL, SDL_MapRGB(gScreenSurface->format, 0, 0, 0));
SDL_BlitSurface(gHelloWorld, NULL, gScreenSurface, NULL);
SDL_UpdateWindowSurface(gWindow);
[...]
}
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