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Xlib - Rotation and interpolation of pixmap - Performance problems

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# 1  
Old 07-14-2014
Xlib - Rotation and interpolation of pixmap - Performance problems
I need to rotate a pixmap in XLib with some kind of interpolation to reduce the aliasing.

I came up with the following code, which uses bilinear interpolation. It works fine: the rotated image looks perfect, but unfortunately it takes 5 or 6 seconds for each rotation. (in a 300x300, 16 colours pixmap)

The following is the code I am using:
Code:
#define CONST (double)((double)180/M_PI)

        cx = attrib.width/2;
        cy = attrib.height/2;

        unsigned long tleft_p, tright_p, bleft_p, bright_p;
        unsigned long background_p;
        XColor tleft_c, tright_c, bleft_c, bright_c;


        Display *dpy = XtDisplay(w);
        Colormap cmap = DefaultColormap(dpy, DefaultScreen(dpy));


        for (y=1; y<attrib.height; y++) {
                for (x=1; x<attrib.width; x++) {
                        XColor mycol;
                        int xx, yy, floor_x, floor_y, ceil_x, ceil_y;
                        float dist, ang, true_x, true_y, delta_x, delta_y;
                        float tred, tgreen, tblue, bred, bgreen, bblue;
                        int red, green, blue;

                        /* rotation */
                        xx = x - attrib.width/2;
                        yy = y - attrib.height/2;
                        true_x = (double)xx * cos((double)deg/CONST) + (double)yy * sin((double)deg/CONST);
                        true_y = (double)xx * -sin((double)deg/CONST) + (double)yy * cos((double)deg/CONST);
 
                        true_x += attrib.height/2;
                        true_y += attrib.width/2;
        
                        floor_x = (int)floor(true_x);
                        floor_y = (int)floor(true_y);
                        ceil_x = (int)ceil(true_x);
                        ceil_y = (int)ceil(true_y);
        
                        delta_x = true_x - (double)floor_x;
                        delta_y = true_y - (double)floor_y;
        
                        tleft_p = XGetPixel(src, floor_x, floor_y);
                        tright_p = XGetPixel(src, ceil_x, floor_y);
                        bleft_p = XGetPixel(src, floor_x, ceil_y);
                        bright_p = XGetPixel(src, ceil_x, ceil_y);
        
                        tleft_c.pixel = tleft_p;
                        tright_c.pixel= tright_p;
                        bleft_c.pixel = bleft_p;
                        bright_c.pixel= bright_p;
                        XQueryColor(dpy, cmap, &tleft_c);
                        XQueryColor(dpy, cmap, &tright_c); 
                        XQueryColor(dpy, cmap, &bleft_c);
                        XQueryColor(dpy, cmap, &bright_c);

                        /* interpolation */
                        /* tred = top red,  bred = bottom red ... */
                        tred = (1-delta_x)* (int)tleft_c.red + delta_x * tright_c.red;
                        tgreen = (1-delta_x)* (int)tleft_c.green + delta_x * tright_c.green;
                        tblue = (1-delta_x)* (int)tleft_c.blue + delta_x * tright_c.blue;

                        bred = (1-delta_x) * (int)bleft_c.red + delta_x * (int)bright_c.red;
                        bgreen = (1-delta_x)*(int)bleft_c.green+delta_x * (int)bright_c.green;
                        bblue = (1-delta_x)* (int)bleft_c.blue+ delta_x * (int)bright_c.blue;

                        red = (int)round((1-delta_y) * tred + delta_y * bred);
                        green = (int)round((1-delta_y) * tgreen + delta_y * bgreen);
                        blue = (int)round((1-delta_y) * tblue + delta_y * bblue);

                        if (red < 0) red = 0;
                        if (green<0) green=0;
                        if (blue<0)  blue =0;
                        if (blue>65535) blue=65535;
                        if (green>65535) green=65535;
                        if (red>65535) red=65535;

                        mycol.red = red;
                        mycol.green=green;
                        mycol.blue=blue;
                        XAllocColor(dpy, cmap, &mycol);

                        XPutPixel(dest, x, y, mycol.pixel);
                }
        }

I attached a working test program, if you wish to try it.
You should link with:
Code:
-lXm -lXt -lX11 -lXp -lXext -lXpm -lm

It requires Motif widget toolkit.

Could you suggest a way to get a reasonable speed?

Thank you very much for your kind help.
--mghis

P.S.: Sorry for my bad English: I'm not a native speaker.
main.c.gz (1.8 KB) 
# 2  
Old 07-14-2014
Aside from algorithmic changes (and those usually result in the best speeding up) I see that sine and cosine functions are called repetitively, so I'd call them once and store result in a local double variable, then use those variables in your formulas, like so:
Code:
 
 cos_var = cos((double)deg/CONST);
 sin_var = sin((double)deg/CONST);
 true_x = true_x = (double)xx * cos_var + (double)yy * sin_var;
 etc...

# 3  
Old 07-14-2014
Thank you, migurus, for your reply.
It did speed it up a bit, but I noticed the problem is mainly in the XAllocColor() call. In fact, if I remove that call and always put a black pixel, (still calculating the values), the program runs at less than half a second per rotation.

However I really don't know to get rid of XAllocColor().

I am writing pixels to an XImage. Is there a way to access directly the RGB values of each pixel?
# 4  
Old 07-16-2014
How are you creating the "dest" XImage? You should probably manipulate the data sent to XCreateImage directly, before calling XCreateImage() to create the dest image.
# 5  
Old 07-17-2014
Src and dest are created with:
Code:
src = XGetImage(dpy, pix, 0, 0, width, height, AllPlanes, ZPixmap);
dest = XGetImage(dpy, pix, 0, 0, width, height, AllPlanes, ZPixmap);

They are both XImages of the Pixmap I need to rotate.
# 6  
Old 07-19-2014
Here's an example of a program that rotates huge images almost instantly:

Simple Image Viewer for Linux/X11: Xiv | Blog L’Ordikc
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