Introduction to SDLDrawing to the screenIf you take a look at my "Setting up Code::Blocks to work with SDL" tutorial, I have already covered drawing a pixel to the screen.
Sooo I'm gonna go ahead and show you how to load and optimise a bitmap.
Note:When writing an SDL program, it is
vital that you remember that main must accept parameters, as follows:
int main (int argc, char *argv[]) or int main (int argc, char **argv)both of which do the same thing.
Remember this! I can't stress enough how important it is... if you don't have args for main, you will get the following error:
undefined reference to winMain@16Here is #1, which will load a bitmap, without optimising:
cpp
#include <SDL/SDL.h> /* Standard SDL include */
const int SCREEN_WIDTH = 640; /* Set the screen width variable */
const int SCREEN_HEIGHT = 480; /* Set the screen height variable */
const int SCREEN_DEPTH = 32; /* Set the screen depth variable */
int main(int argc, char *argv[]) { /* In SDL, all programs 'main' function MUST accept these parameters */
SDL_Surface *screen = NULL; /* The surface on which we will load the screen */
SDL_Surface *bitmap = NULL; /* The surface on which we will load the bitmap */
SDL_Rect offset; /* The rectangle (target area) to which we will load the bitmap */
/* Remember, when we create a pointer, it's always good practice to assign them to NULL */
/* Initialize SDL */
SDL_Init(SDL_INIT_VIDEO);
/* Alternatively, we could use SDL_Init (SDL_INIT_EVERYTHING);
* but, we only need video in this application, so we'll just initialise the video.
* Makes sense, right? */
/* Initialise the screen, by passing the screen width, height, depth, and surface type */
screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_DEPTH, SDL_SWSURFACE);
/* Two of the common surface types are:
* SDL_SWSURFACE - which will load the main screen surface as a window
* SDL_FULLSCREEN - which will load the application in full screen */
/* Now to set up the offset variables, where we will draw the bitmap to */
offset.x = 0;
offset.y = 0;
offset.h = SCREEN_HEIGHT;
offset.w = SCREEN_WIDTH;
/* Now to witness the supreme power of SDL when you want to load an image... ONE LINE! */
bitmap = SDL_LoadBMP ("myBMP.bmp");
/* Now we need to apply the bitmap to the screen... the syntax is:
* SDL_BlitSurface (SDL_Surface*, SDL_Rect, SDL_Surface*, SDL_Rect*) */
SDL_BlitSurface (bitmap, NULL, screen, &offset);
/* update the screen (aka double buffering) */
SDL_Flip(screen);
while(true); /* Infinite loop, just to keep the window open here */
}
Now, when we want to optimise the surface, we need to make a call to one of my snippets, which can be found
hereAdd that function in, and change
bitmap = SDL_LoadBMP ("myBMP.bmp"); to
bitmap = Load_Optimal("myBMP.bmp");The final code should look like this:
cpp
#include <SDL/SDL.h> /* Standard SDL include */
const int SCREEN_WIDTH = 640; /* Set the screen width variable */
const int SCREEN_HEIGHT = 480; /* Set the screen height variable */
const int SCREEN_DEPTH = 32; /* Set the screen depth variable */
SDL_Surface *Load_Optimal (char *filename); /* Function prototype, to return an optimised image */
int main(int argc, char *argv[]) { /* In SDL, all programs 'main' function MUST accept these parameters */
SDL_Surface *screen = NULL; /* The surface on which we will load the screen */
SDL_Surface *bitmap = NULL; /* The surface on which we will load the bitmap */
SDL_Rect offset; /* The rectangle (target area) to which we will load the bitmap */
/* Remember, when we create a pointer, it's always good practice to assign them to NULL */
/* Initialize SDL */
SDL_Init(SDL_INIT_VIDEO);
/* Alternatively, we could use SDL_Init (SDL_INIT_EVERYTHING);
* but, we only need video in this application, so we'll just initialise the video.
* Makes sense, right? */
/* Initialise the screen, by passing the screen width, height, depth, and surface type */
screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_DEPTH, SDL_SWSURFACE);
/* Two of the common surface types are:
* SDL_SWSURFACE - which will load the main screen surface as a window
* SDL_FULLSCREEN - which will load the application in full screen */
/* Now to set up the offset variables, where we will draw the bitmap to */
offset.x = 0;
offset.y = 0;
offset.h = SCREEN_HEIGHT;
offset.w = SCREEN_WIDTH;
/* Now to witness the supreme power of SDL when you want to load an image... ONE LINE! */
bitmap = Load_Optimal ("myBMP.bmp");
/* Now we need to apply the bitmap to the screen... the syntax is:
* SDL_BlitSurface (SDL_Surface*, SDL_Rect*, SDL_Surface*, SDL_Rect*) */
SDL_BlitSurface (bitmap, NULL, screen, &offset);
/* update the screen (aka double buffering) */
SDL_Flip(screen);
while(true); /* Infinite loop, just to keep the window open here */
}
SDL_Surface *Load_Optimal (char *filename)
{
SDL_Surface *loaded = NULL; /* The surface to load the basic image */
SDL_Surface *optimal = NULL; /* The optimised surface */
loaded = SDL_LoadBMP (filename); /* Load the basic image */
if (loaded != NULL) /* This is why NULL is important, now we can check if it was loaded successfully */
{
optimal = SDL_DisplayFormat (loaded); /* Load an optimised version of the basic surface */
SDL_FreeSurface (loaded); /* Delete the basic one, it's no longer needed */
}
return optimal; /* Return the optimised image */
)
Attached is the bitmap that I loaded in the sample:
myBMP.bmp ( 301.05k )
Number of downloads: 12Edit: Added a note about main, it
has to accept parameters!
Intro to SDL, Loading and optimising bitmaps
11 Jul, 2008 - 10:25 AM
|