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libi3: add logical_px() for Retina display support

This commit is contained in:
Michael Stapelberg 2014-04-26 17:17:37 +02:00
parent a0e979d097
commit c79c49f69d
2 changed files with 24 additions and 0 deletions
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8
include/libi3.h
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@ -381,3 +381,11 @@ char *get_process_filename(const char *prefix);
* Returned value must be freed by the caller.
*/
char *get_exe_path(const char *argv0);
/**
* Convert a logical amount of pixels (e.g. 2 pixels on a “standard” 96 DPI
* screen) to a corresponding amount of physical pixels on a standard or retina
* screen, e.g. 5 pixels on a 227 DPI MacBook Pro 13" Retina screen.
*
*/
int logical_px(const int logical);

16
libi3/dpi.c Normal file
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@ -0,0 +1,16 @@
#include "libi3.h"
#include <math.h>
extern xcb_screen_t *root_screen;
/*
* Convert a logical amount of pixels (e.g. 2 pixels on a “standard” 96 DPI
* screen) to a corresponding amount of physical pixels on a standard or retina
* screen, e.g. 5 pixels on a 227 DPI MacBook Pro 13" Retina screen.
*
*/
int logical_px(const int logical) {
const double dpi = (double)root_screen->height_in_pixels * 25.4 /
(double)root_screen->height_in_millimeters;
return ceil((dpi / 96.0) * logical);
}