Thread: Draw line with multicolor

Hello. I need draw many lines with multicolor (color is set bysome pixmap (xpm))
on C++ with standart libs.

Horizontal lines are drawing succsessfully with GC and XSetTile.
But non-horizontal - no good. I rotate pixmap for all lines and then
XSetTile for each line with own pixmap, but it's bad idea.

How I can do this with standard libraries (xlib only. Without Qt, OpenGL etc.)?

Done.
For calculate lines used Bresenham's algorithm.

Code:

#include <math.h>
#include <X11/Xlib.h>
#include <X11/xpm.h>
#include <stdlib.h>


void XDrawLineFillXpm(XPoint start, XPoint end,
               Display *disp, Drawable d, GC gc, Pixmap pmap, Pixmap mask)
{    
    signed char dir[2];     // direction of the line ([0]:x; [1]:y)
    unsigned short delta[2];   // dx; dy
    unsigned char base = 0;   // base coord (that changed faster)
    short error;      // sum error
    short pos[2][2];  // curr & end positions


    static Pixmap currPmap = NULL;  // color of line
    static XpmImage xpmImage;       // xpm color of line
    unsigned short currColor = 0;
    unsigned short currLine = 0;
    static unsigned short currXInd = 0;
    char colorHex[6];
    static unsigned long *colorLong = NULL;
    unsigned int prevIndex = 0;
    unsigned short startCoord = 0;
    unsigned short val = 0;
    static XPoint prevEndPoint = {-1,-1};


    if (prevEndPoint.x != start.x
            || prevEndPoint.y != start.y)
        prevIndex = 0;
    else
        prevIndex = currXInd;


    // New pixmap? -> Read color & xpm
    if (currPmap != pmap)
    {
        currPmap = pmap;
        XpmCreateXpmImageFromPixmap(disp, pmap, mask, &xpmImage, NULL);


        if (colorLong != NULL)
            free(colorLong);
        colorLong = (unsigned long*)malloc(xpmImage.ncolors);


        for (currXInd = 0; currXInd < xpmImage.ncolors; currXInd++)
        {
            colorHex[0] = xpmImage.colorTable[currXInd].c_color[1];
            colorHex[1] = xpmImage.colorTable[currXInd].c_color[2];
            colorHex[2] = xpmImage.colorTable[currXInd].c_color[5];
            colorHex[3] = xpmImage.colorTable[currXInd].c_color[6];
            colorHex[4] = xpmImage.colorTable[currXInd].c_color[9];
            colorHex[5] = xpmImage.colorTable[currXInd].c_color[10];


            colorLong[currXInd] = strtol(colorHex, NULL, 16);
        }
        currXInd = 0;
    }


    // take direction
    delta[0] = (end.x > start.x ? (dir[0] = 1, end.x - start.x)
                                    : (dir[0] = -1, start.x - end.x)) << 1; //*2
    delta[1] = (end.y > start.y ? (dir[1] = 1, end.y - start.y)
                                    : (dir[1] = -1, start.y - end.y)) << 1;


    // If 'y' changed faster than 'x'
    if (delta[1] > delta[0])
        base = 1;


    XSetFillStyle(disp, gc, FillSolid);


    // Num of lines = Height
    for (currLine = 0; currLine < xpmImage.height; currLine++)
    {
        if (xpmImage.height > 1)
            startCoord = (xpmImage.height >> 1) - currLine;
        else
            startCoord = 0;


        // Fill all colors for each line
        for (currColor = 0; currColor < xpmImage.ncolors; currColor++)
        {
            pos[0][0] = start.x;
            pos[0][1] = start.y;
            pos[1][0] = end.x;
            pos[1][1] = end.y;


            // Recalculate start & end points
            if (base) // y is base coord
            {
                val = startCoord*dir[base];
                pos[0][1-base] += val;
                pos[1][1-base] += val;
            }
            else // x is base coord
            {
                val = startCoord*dir[base]*(-1);
                pos[0][1-base] += val;
                pos[1][1-base] += val;
            }


            // Set new color for points
            XSetForeground(disp, gc, colorLong[currColor]);
            currXInd = prevIndex; // load previous index for each color


            if (xpmImage.data[currLine*xpmImage.width + currXInd++] ==
                    currColor)
                XDrawPoint(disp, d, gc, pos[0][0], pos[0][1]);


            if (currXInd >= xpmImage.width)
                currXInd = 0;


            error = delta[1-base] - (delta[base] >> 1);


            while(pos[0][base] != pos[1][base])
            {
                if (error >= 0)
                {
                    if (error || dir[base] > 0)
                    {
                        pos[0][1-base] += dir[1-base]; //change pos by no-base
                        error -=delta[base];
                    }
                }


                pos[0][base] += dir[base];  // change pos by base coord
                error += delta[1-base];


                if (xpmImage.data[currLine*xpmImage.width + currXInd++] == currColor)
                    XDrawPoint(disp, d, gc, pos[0][0], pos[0][1]);
                if (currXInd >= xpmImage.width)
                    currXInd = 0;
            }
        }
    }


    prevEndPoint = end;
}