## Tcl8.6.15/Tk8.6.15 Documentation > Tk C API, version 8.6.15 > GetPixels

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  NAME
    Tk_GetPixelsFromObj, Tk_GetPixels, Tk_GetMMFromObj, Tk_GetScreenMM — translate between strings and screen units
  SYNOPSIS
    #include <tk.h>
    int
    Tk_GetPixelsFromObj(interp, tkwin, objPtr, intPtr)
    int
    Tk_GetPixels(interp, tkwin, string, intPtr)
    int
    Tk_GetMMFromObj(interp, tkwin, objPtr, doublePtr)
    int
    Tk_GetScreenMM(interp, tkwin, string, doublePtr)
  ARGUMENTS
  DESCRIPTION
    <none>
    c
    i
    m
    p
  KEYWORDS

### NAME

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

### SYNOPSIS

#include <tk.h>
int
Tk_GetPixelsFromObj(interp, tkwin, objPtr, intPtr)
int
Tk_GetPixels(interp, tkwin, string, intPtr)
int
Tk_GetMMFromObj(interp, tkwin, objPtr, doublePtr)
int
Tk_GetScreenMM(interp, tkwin, string, doublePtr)

### ARGUMENTS

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.

### DESCRIPTION

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:

<none>
  The number specifies a distance in pixels.

c
  The number specifies a distance in centimeters on the screen.

i
  The number specifies a distance in inches on the screen.

m
  The number specifies a distance in millimeters on the screen.

p
  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_GetPixels 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.

### KEYWORDS

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