---
name: "Tk_GetMMFromObj"
section: "3tk"
platform: "linux"
package: "tk8.6-doc"
version: "8.6.16-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Tk_GetPixelsFromObj/3tk"
---

# Tk\_GetMMFromObj(3tk)

translate between strings and screen units

Part of [Tk\_GetPixelsFromObj(3tk)](/Tk_GetPixelsFromObj/3tk.md).

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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

- 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