Tk_GetPixelsFromObj, Tk_GetPixels, Tk_GetMMFromObj, Tk_GetScreenMM − translate between strings and screen units


#include <tk.h>

interp, tkwin, objPtr, intPtr)

interp, tkwin, string, intPtr)

interp, tkwin, objPtr, doublePtr)

interp, tkwin, string, doublePtr)


Tcl_Interp *interp (in)

Interpreter to use for error reporting.

Tk_Window tkwin (in)

Window whose screen geometry determines the conversion between absolute units and pixels.

Tcl_Obj *objPtr (in/out)

String value specifies a distance on the screen; internal rep will be modified to cache converted distance.

const char *string (in)

Same as objPtr except specification of distance is passed as a string.

int *intPtr (out)

Pointer to location in which to store converted distance in pixels.

double *doublePtr (out)

Pointer to location in which to store converted distance in millimeters.



These procedures take as argument a specification of distance on the screen (objPtr or string) and compute the corresponding distance either in integer pixels or floating-point millimeters. In either case, objPtr or string specifies a screen distance as a floating-point number followed by one of the following characters that indicates units:


The number specifies a distance in pixels.


The number specifies a distance in centimeters on the screen.


The number specifies a distance in inches on the screen.


The number specifies a distance in millimeters on the screen.


The number specifies a distance in printer’s points (1/72 inch) on the screen.

Tk_GetPixelsFromObj converts the value of objPtr to the nearest even number of pixels and stores that value at *intPtr. It returns TCL_OK under normal circumstances. If an error occurs (e.g. objPtr contains a number followed by a character that is not one of the ones above) then TCL_ERROR is returned and an error message is left in interp’s result if interp is not NULL. Tk_GetPixelsFromObj caches information about the return value in objPtr, which speeds up future calls to Tk_GetPixelsFromObj with the same objPtr.

Tk_GetPixels is identical to Tk_GetPixelsFromObj except that the screen distance is specified with a string instead of an object. This prevents Tk_GetPixels from caching the return value, so Tk_GetAnchor is less efficient than Tk_GetPixelsFromObj.

Tk_GetMMFromObj and Tk_GetScreenMM are similar to Tk_GetPixelsFromObj and Tk_GetPixels (respectively) except that they convert the screen distance to millimeters and store a double-precision floating-point result at *doublePtr.


centimeters, convert, inches, millimeters, pixels, points, screen units

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