Michael Samuel wrote:
Ok, this question is quite a simple one (I hope)…
I want to make a very simple widget set for a program I’m writing (eg. buttons
and writing to go on them), and I feel rather silly drawing a BMP for each
oneI read the example in the docs of writing a single pixel, but that didn’t give
me any (workable) ideas on how to draw to the screen.Anyway, could somebody give me some examples of how to do the following things:
- Draw a square, and fill in with a different colour to the outline
First off…don’t use that disgusting screenlib…avoid the yucky C++ altogether
and just do it yourself!
Second off, to set a pixel on the screen do this:
*(surface->pixels + (y * WIDTH) + x) = pixel;
Where:
x is the x location of the area you want to set the pixel.
y…(ditto)
WIDTH is the width of the screen in pixels. (You could replace that with
surface->pitch, make sure to use 8 bit display)
pixel is the color you want to set the pixel to. NOTE: Make sure to set palette!
surface is the SDL_Surface you want to put the pixel on.
NOTE: these functions are intended to run on an 8 bit display. Also, these
functions are NOT optimized. You should look for faster equivalents.
Make a function to draw a horizontal line:
We only need a x, y, and another x value. (the other y value will be the same
cause it’s horizontal!)
void
Horiz_Line (SDL_Surface * surface, int x1, int y1, int x2, char color)
{
Uint8 *pixel;
pixel = surface->pixels + (y1 * screen->pitch) + x1;
/* x1, and x2, CHECK values for validity (e.g. x1= 2, x2 MUST be more than x1!, x1
must be less than x2! (or equal) */
while (x1 <= x2)
{
*pixel = color;
++pixel;
++x1;
}
}
Now make a function to draw a vertical line, only this time add the width of the
surface instead of 1 to the pointer.
We only need a x, y, and second y value here.
void
Verti_Line (SDL_Surface *surface, int x1, int y1, int y2, char color)
{
Uint8 *pixel;
pixel = surface->pixels + (y1 * screen->pitch) + x1;
/* make sure to check validity of y1, and y2 */
while (y1 <= y2)
{
*pixel = color;
pixel += screen->pitch;
++y1;
}
}
To draw a filled box do this:
void
Fill_Box (SDL_Surface * surface, int x1, int y1, int x2, int y2, char color)
{
while (y1 <= y2)
{
/* You could use the code in Horiz_Line here if you want a faster line without the
function call overhead /
/ memset would work here too as a replacement for horizline, would memset be
faster? /
/ You might also consider some error checking to make sure y1 is less than or
equal to y2.
Horiz_Line (surface, x1, y1, x2, color);
y1++;
}
}
Now. If you want to draw a outlined box do this:
void
Empty_Box (SDL_Surface *surface, int x1, int y1, int x2, int y2, char color)
{
Horiz_Line (surface, x1, y1, x2, color);
Horiz_Line (surface, x1, y2, x2, color);
Verti_Line (surface, x1, y1, y2, color);
Verti_Line (surface, x2, y1, y2, color);
}
Ok, so now you have your vertical and horizonal line drawing systems, and outlined
box func and a fill box func.
do this to get that effect you want:
(1)draw a filled box
(2)draw an outlined box in the same place over it.
It should work. Let me know if it does.
- Draw a circle
Don’t draw circles! I mean it!
If I could understand how that’s done, I can probably start writing almost-
good programs
Now write DAMN good programs NOW! And tell me about them! I had a lot of trouble
understanding writing to the screen myself so you are not alone.
–
– Michael Samuel
Paul Lowe
xpaull at ultraviolet.org
