Array Program Help

[wvu2005]

Hi everyone. This is my first post.

I'm trying to malloc space for a color image in memory, fill it with a design like a colored rectangle, and then write it out into a PPM format file (which will be done in Unix).

As a note, I've had very little experience with 3D arrays. However, I know that the image in memory acts like a 3D array except that the pointers only let you access it one dimension. Any help would be greatly appreciated. I thought this would be a neat thing to try to do (I wanted to ultimately try to make a checkerboard in the long term, but I'm having trouble making a simple colored rectangle, haha).

Below is what I've written so far, I'm kind of stumped on where to go from there. I've commented a section where I believe that the code would go to generate the image.

 
#include <stdio.h>
#include <stdlib.h>
main(int argc, char *argv[]) {
	unsigned char *image, *tempptr;
	int x, y, c, width, height;
	if(argc < 3) {
		fprintf(stderr, "Usage: %s width height\n", argv[0]);
		exit(1);
	}
	width = atoi(argv[1]);
	height = atoi(argv[2]);
// ***** I believe this is where I should add the code to   
              generate the image and write it   
              out as a PPM file
	return(0);
}

Thank you for your help,
James

[Salem]

> However, I know that the image in memory acts like a 3D array
Width and height is 2D - what's the 3rd?

[wvu2005]

Color would be the 3rd dimension of the array (e.g. a rectangle consisting of values for length and width would be two dimensions and the coloring of it would be the 3rd).


Thanks,
James

[bithub]

No, the color would be the array element value.

pixel[width][height] = someColor;

[Ancient Dragon]

maybe width, height and depth?

// This is a 3d array.
pixel[width][height][depth] = someColor;

[bithub]

Depth is just the number of bits used to define a color. 32 bit vs 24 bit vs 16 bit etc.

[wvu2005]

Hi everyone,

Thank you all for following up with my question. I still am in need of help, but I did not know that depth would be used to define the color, that's very interesting (I stand corrected bithub ).


Thanks again,
James

[wvu2005]

Hi,

I've made some progress. I can generate the color, but still can't generate the rectangle. Below is my code:

#include <stdio.h>
#include <stdlib.h>


//drawPixel function
//added to simplify drawing loops below 
void drawPixel(unsigned char *picPointer, int picWidth, int x, int y, unsigned char
rVal, unsigned char gVal, unsigned char bVal)
{

        picPointer[3*y*picWidth + 3*x] = rVal; //+0 to access red byte
        picPointer[3*y*picWidth + 3*x + 1] = gVal; //+1 to access green byte
        picPointer[3*y*picWidth + 3*x + 2] = bVal; //+2 to access blue byte

return;
}


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

if (argc < 3)
{
        fprintf(stderr, "Usage: %s width height\n", argv[0]);
        exit(1);
}

const int wid = atoi(argv[1]); 
const int ht = atoi(argv[2]); 

unsigned char *picture = (unsigned char *) malloc(3*wid*ht*sizeof(unsigned char));

int x,y;

for(y=0;y<ht;y++)
{

        for(x=0;x<wid;x++)
        {
                drawPixel(picture,wid,x,y,60,100,200); //fills whole image with a light blue
        }

As always, any help is greatly appreciated.

Thanks.