Jump to content
  • Advertisement

Archived

This topic is now archived and is closed to further replies.

jmg5

SDL - getting the image to move

This topic is 5425 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Been reading up on SDL for awhile, and finally got a bitmap to load on the screen. Now, I want to move it up and down with the arrow keys. I got a variable YPOS, and I update it in the game loop when a key is pressed. But how do I tell SDL to know I want the image to go up and down? How do I assign YPOS to the image?
#include <stdio.h>
#include <stdlib.h>
#include <SDL/SDL.h>

SDL_Surface *screen;
SDL_Surface *image;
SDL_Event event;
int ypos=0;

void display_bmp(SDL_Surface *image)
{
    image = SDL_LoadBMP("paddle.bmp");
    if (image == NULL) {
        printf("Could Not Load Bitmap: %s\n", SDL_GetError());
        return;
    }

    if(SDL_BlitSurface(image, NULL, screen, NULL) < 0)
        printf("BlitSurface Error: %s\n", SDL_GetError());

    SDL_UpdateRect(screen, 0, 0, image->w, image->h);
    SDL_FreeSurface(image);
}

int main(int argc, char *argv[])
{   
    Uint8* keys;

    if (SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO) < 0)
    {
        printf("Could Not Initialize SDL: %s", SDL_GetError());
        exit(1);
    }
    atexit(SDL_Quit);
    
    screen = SDL_SetVideoMode(800, 600, 32, SDL_SWSURFACE);
    if (screen == NULL)
    {
        printf("Could Not Use 800x600 Video Mode: %s", SDL_GetError());
        exit(1);
    }
 
    int done=1;
    while(done)
    {
        while (SDL_PollEvent(&event))
        {
            if (event.type == SDL_QUIT) {done = 0;}

            if (event.type == SDL_KEYDOWN)
            {
                keys = SDL_GetKeyState(NULL);
                if (keys[SDLK_UP]) {ypos -= 1;}
                if (keys[SDLK_DOWN]) {ypos += 1;}
            }
        }
        display_bmp(image);
    }
    return 0;
}
That''s what I have so far. I can''t figure out a way to make the image move. I think it may have something to do with the SDL_UpdateRect function. All help is appreciated.

Share this post


Link to post
Share on other sites
Advertisement
Guest Anonymous Poster
this simple program can help

#include "SDL.h"
#include <math.h>

int main(int argc, char *argv[])
{
SDL_Surface *Display;
SDL_Surface *bmpGoylel;
SDL_Event Event;
SDL_Rect SrcRect, DstRect;
SDL_Rect Velocity;

const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;

SDL_Init(SDL_INIT_VIDEO);

Display = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, 16,
SDL_FULLSCREEN|SDL_DOUBLEBUF);
bmpGoylel = SDL_LoadBMP("goylel.bmp");

SrcRect.w = DstRect.w = bmpGoylel->w;
SrcRect.h = DstRect.h = bmpGoylel->h;
SrcRect.x = SrcRect.y = DstRect.x = DstRect.y = Velocity.x = Velocity.y = 0;

for(;;)
{
if(SDL_PollEvent(&Event) == 0)
{
DstRect.x += Velocity.x;
DstRect.y += Velocity.y;

//collision detection on the screen

if(DstRect.x <= 0)
Velocity.x = abs(Velocity.x);
if(DstRect.y <= 0)
Velocity.y = abs(Velocity.y);
if(DstRect.x >= SCREEN_WIDTH - DstRect.w)
Velocity.x = -abs(Velocity.x);
if(DstRect.y >= SCREEN_HEIGHT - DstRect.h)
Velocity.y = -abs(Velocity.y);

SDL_FillRect(Display, NULL, 0);
SDL_BlitSurface(bmpGoylel, &SrcRect, Display, &DstRect);

SDL_Flip(Display);
}
else
{
if(Event.type == SDL_KEYDOWN)
{
//movement actions

switch(Event.key.keysym.sym)
{
case SDLK_UP:
Velocity.y--;
break;
case SDLK_DOWN:
Velocity.y++;
break;
case SDLK_RIGHT:
Velocity.x++;
break;
case SDLK_LEFT:
Velocity.x--;
break;
case SDLK_SPACE:
Velocity.x = Velocity.y = 0;
break;
}

if(Event.key.keysym.sym == SDLK_ESCAPE)
break;//break out of loop

}

if(Event.type == SDL_QUIT)
break;
}
}
return 0;
}

Share this post


Link to post
Share on other sites
Basically, images don''t move. However, the position on the screen that you copy it to can change.

Share this post


Link to post
Share on other sites

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

Participate in the game development conversation and more when you create an account on GameDev.net!

Sign me up!