This should be slightly easier to read:
Display*X_display = NULL;
Window X_mainWindow;
ColormapX_cmap;
Visual* X_visual;
GC X_gc;
int X_screen;
XVisualInfo X_visualinfo;
XImage* image = NULL;
int X_width;
int X_height;
unsigned long st2d_8to24table[256];
int32_t shiftmask_fl = 0;
int32_t r_shift, g_shift, b_shift;
uint32_t r_mask, g_mask, b_mask;
//
// I_InitGraphics
//
// Creates and maps window
void I_InitGraphics (void)
{
char* displayname = NULL;
X_width = SCREENWIDTH;
X_height = SCREENHEIGHT;
// open the display
X_display = XOpenDisplay(displayname);
// use the default visual
X_screen = DefaultScreen(X_display);
XMatchVisualInfo(X_display, X_screen, 24, TrueColor, _visualinfo);
X_visual = X_visualinfo.visual;
// create the main window
X_mainWindow = XCreateWindow(X_display,
RootWindow(X_display, X_screen),
0, 0,
X_width, X_height,
0, // borderwidth
X_visualinfo.depth, // depth
InputOutput,
X_visual,
0,
0);
// create the GC
X_gc = XCreateGC(X_display,
X_mainWindow,
0,
NULL);
// map the window
XMapWindow(X_display, X_mainWindow);
image = XCreateImage(X_display,
X_visual,
X_visualinfo.depth,
ZPixmap,
0,
malloc((X_width * 4) * X_height),
X_width, X_height,
32,
0);
screens[0] = (byte *)image->data;
}
// Convert colors to 24 bits, called by I_FinishUpdate()
void st3_fixup (int width, int height)
{
uint8_t *row_src;
for (int y = 0; y < height; y++) {
row_src = (uint8_t *)>data [y * image->bytes_per_line];
for (int x = width-1; x >= 0; x--) {
XPutPixel(image, x, y, st2d_8to24table[row_src[x]]);
}
}
}
// Called by xlib_rgb24()
void shiftmask_init (void)
{
unsigned int x;
r_mask = X_visual->red_mask;
g_mask = X_visual->green_mask;
b_mask = X_visual->blue_mask;
for (r_shift = -8, x = 1; x < r_mask; x = x << 1)
r_shift++;
for (g_shift = -8, x = 1; x < g_mask; x = x << 1)
g_shift++;
for (b_shift = -8, x = 1; x < b_mask; x = x << 1)
b_shift++;
shiftmask_fl = 1;
}
// Called by UploadNewPalette()
unsigned long xlib_rgb24 (int r, int g, int b)
{
unsigned long p;
if (shiftmask_fl == 0)
shiftmask_init();
p = 0;
if (r_shift > 0) {
p = (r << (r_shift)) & r_mask;
} else if (r_shift < 0) {
p = (r >> (-r_shift)) & r_mask;
} else p |= (r & r_mask);
if (g_shift > 0) {
p |= (g << (g_shift)) & g_mask;
} else if (g_shift < 0) {
p |= (g >> (-g_shift)) & g_mask;
} else p |= (g & g_mask);
if (b_shift > 0) {
p |= (b << (b_shift)) & b_mask;
} else if (b_shift < 0) {
p |=(b >> (-b_shift)) & b_mask;
} else p |= (b & b_mask);
return p;
}
//
// Palette stuff.
//
void UploadNewPalette (Colormap cmap, byte *palette)
{
(void)cmap; // UNUSED
for (int i = 0; i < 256; i++)
{
st2d_8to24table[i] = xlib_rgb24(palette[i * 3], palette[i * 3 +
1],palette[i * 3 + 2]);
}
}
//
// I_SetPalette
//
void I_SetPalette (byte* palette)
{
UploadNewPalette(X_cmap, palette);
}
//
// I_FinishUpdate
//
// Display the image on the window
void I_FinishUpdate (void)
{
// Convert colors of the image to 24 bits color depth
st3_fixup(X_width, X_height);
// draw the image
XPutImage(X_display,
X_mainWindow,
X_gc,
image,
0, 0,
0, 0,
X_width, X_height );
// sync up with server
XSync(X_display, False);
}
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