Togl - a Tk OpenGL widget

Version 1.3

Copyright (C) 1996-1997 Brian Paul and Ben Bederson



Introduction

Togl is a Tk widget for OpenGL rendering. Togl is originally based on OGLTK, written by Benjamin Bederson at the University of New Mexico. Togl adds the new features:

Togl allows one to create and manage a special Tk/OpenGL widget with Tcl and render into it with a C program. That is, a typical Togl program will have Tcl code for managing the user interface and a C program for computations and OpenGL rendering.

Togl is copyrighted by Brian Paul (brianp@elastic.avid.com) and Benjamin Bederson (bederson@cs.unm.edu). See the LICENSE file for details.

The Togl WWW page is available from:

Prerequisites

You should have Tcl and Tk installed on your computer, including the Tk source code files. Togl has been tested with Tcl 7.4/Tk 4.0, Tcl 7.5/Tk 4.1 and Tcl 7.6/Tk 4.2 at this time. It is currently configured for Tcl7.6/Tk4.2.

You must also have OpenGL or Mesa (a free alternative to OpenGL) installed on your computer.

One should be familiar with Tcl, Tk, OpenGL, and C programming to use Togl effectively.


Getting Togl

The current version of Togl is 1.3. You may download it from either:

Togl may also be obtained manually with ftp:

The Makefile included with Togl is configured for SGI systems. It shouldn't be hard to adapt it for others. In practice, you'll just add togl.c to your application's Makefile.


Using Togl With Your Application

Since the Togl code is in just three files (togl.c, togl.h and tkInt.h) it's probably most convenient to just include those files with your application sources. The Togl code could be made into a library but that's not necessary.

Togl defines an API of C-callable functions and an API of Tcl-callable functions. The functions are documented here. See the demo programs for examples of how they are used.


C Togl Functions

These are the Togl commands one may call from a C program.

#include "togl.h"

Setup and Initialization Functions

int Togl_Init( Tcl_Interp *interp )
Initializes the Togl module. This is typically called from the Tk_Main() callback function.
void Togl_CreateFunc( Togl_Callback *proc )
void Togl_DisplayFunc( Togl_Callback *proc )
void Togl_ReshapeFunc( Togl_Callback *proc )
void Togl_DestroyFunc( Togl_Callback *proc )
Register C functions to be called by Tcl/Tk when a widget is realized, must be redrawn, is resized, or is destroyed respectively.

Each C callback must be of the form: 

	void callback( struct Togl *togl )
	{
	   ...your code...
	}
void Togl_TimerFunc( Togl_Callback *proc )
Register a C timer callback function which will be called every n milliseconds. The interval n is specified by the -time option to the Togl Tcl command.

The C callback must be of the form: 

	void my_timer_callback( struct Togl *togl )
	{
	   ...your code...
	}
void Togl_CreateCommand( char *cmd_name, Togl_CmdProc *cmd_proc )
Used to create a new Togl sub-command. The C function which implements the command must be of the form: 
	int callback( struct Togl *togl, int argc, char *argv[] )
	{
	   ...your code...
	   return TCL_OK or TCL_ERROR;
	}

Drawing-related Commands

void Togl_PostRedisplay( struct Togl *togl )
Signals that the widget should be redrawn. When Tk is next idle the user's C render callback will be invoked. This is typically called from within a Togl sub-command which was registered with Togl_CreateCommand().
void Togl_SwapBuffers( struct Togl *togl )
Swaps the front and back color buffers for a double-buffered widget. glFlush() is executed if the window is single-buffered. This is typically called in the rendering function which was registered with Togl_DisplayFunc().

Query Functions

char *Togl_Ident( struct Togl *togl )
Returns a pointer to the identification string associated with a Togl widget or NULL if there's no identifier string.
int Togl_Width( struct Togl *togl )
Returns the width of the given Togl widget. Typically called in the function registered with Togl_ReshapeFunc().
int Togl_Height( struct Togl *togl )
Returns the height of the given Togl widget. Typically called in the function registered with Togl_ReshapeFunc().
Tcl_Interp *Togl_Interp( struct Togl *togl )
Returns the Tcl interpreter associated with the given Togl widget.

Color Index Mode Functions

These functions are only used for color index mode.

unsigned long Togl_AllocColor( struct Togl *togl, float red, float green, float blue )
Allocate a color from a read-only colormap. Given a color specified by red, green, and blue return a colormap index (aka pixel value) whose entry most closely matches the red, green, blue color. Red, green, and blue are values in [0,1]. This function is only used in color index mode when the -privatecmap option is false.
void Togl_FreeColor( struct Togl *togl, unsigned long index )
Free a color in a read-only colormap. Index is a value which was returned by the Togl_AllocColor() function. This function is only used in color index mode when the -privatecmap option is false.
void Togl_SetColor( struct Togl *togl, int index, float red, float green, float blue )
Load the colormap entry specified by index with the given red, green and blue values. Red, green, and blue are values in [0,1]. This function is only used in color index mode when the -privatecmap option is true.

Font Functions

GLuint Togl_LoadBitmapFont( struct Togl *togl, const char *fontname )
Load the named font as a set of glBitmap display lists. fontname may be one of Zero is returned if this function fails.

After Togl_LoadBitmapFont() has been called, returning fontbase, you can render a string s with:
glListBase( fontbase );
glCallLists( strlen(s), GL_BYTE, s );

To maximize the portability of your application it is best to use one of the predefined TOGL_BITMAP_* fonts.
void Togl_UnloadBitmapFont( struct Togl *togl, GLuint fontbase )
Destroys the bitmap display lists created by by Togl_LoadBitmapFont().

Client Data Functions

void Togl_SetClientData( struct Togl *togl, ClientData clientData)
clientData is a pointer to an arbitrary user data structure. Each Togl struct has such a pointer. This function sets the Togl widget's client data pointer.
ClientData Togl_GetClientData( const struct Togl *togl )
clientData is a pointer to an arbitrary user data structure. Each Togl struct has such a pointer. This function returns the Togl widget's client data pointer.

Overlay Functions

These functions are modelled after GLUT's overlay sub-API.

void Togl_UseLayer( struct Togl *togl, int layer )
Select the layer into which subsequent OpenGL rendering will be directed. layer may be either TOGL_OVERLAY or TOGL_NORMAL.
void Togl_ShowOverlay( struct Togl *togl )
Display the overlay planes, if any.
void Togl_HideOverlay( struct Togl *togl )
Hide the overlay planes, if any.
void Togl_PostOverlayRedisplay( struct Togl *togl )
Signal that the overlay planes should be redraw. When Tk is next idle the user's C overlay display callback will be invoked. This is typically called from within a Togl sub-command which was registered with Togl_CreateCommand().
void Togl_OverlayDisplayFunc( Togl_Callback *proc )
Registers the C callback function which should be called to redraw the overlay planes. This is the function which will be called in response to Togl_PostOverlayRedisplay(). The callback must be of the form: 
	void RedrawOverlay( struct Togl *togl )
	{
	   ...your code...
	}
int Togl_ExistsOverlay( struct Togl *togl )
Returns 1 if overlay planes exist, 0 otherwise.
int Togl_GetOverlayTransparentValue( const struct Togl *togl )
Returns the color index of the overlay's transparent pixel value.
int Togl_IsMappedOverlay( const struct Togl *togl )
Returns 1 if the overlay planes are currently displayed, 0 otherwise.
unsigned long Togl_AllocColorOverlay( const struct Togl *togl, float red, float green, float blue )
Allocate a color in the overlay planes. Red, green, and blue are values in [0,1]. Return the color index or -1 if the allocation fails.
void Togl_FreeColorOverlay( const struct Togl *togl, unsigned long index )
Free a color which was allocated with Togl_AllocColorOverlay().

X11-only Functions

These functions are only implemented on systems using the X Window System. We recommend that you avoid using these functions in your application since they are not portable to other operating/window systems.

If you choose to use these functions in your application your must first define the TOGL_X11 preprocessor symbol before including the Togl header file: 

    #define TOGL_X11
    #include "Togl.h"
Display *Togl_Display( const struct Togl *togl )
Returns the X Display of a Togl widget.
Screen *Togl_Screen( const struct Togl *togl )
Returns the X Screen of a Togl widget.
int Togl_ScreenNumber( const struct Togl *togl )
Returns the X screen number of a Togl widget.
Colormap Togl_Colormap( const struct Togl *togl )
Returns the X Colormap used by a Togl widget.

Postscript Output

int Togl_DumpToEpsFile( const struct Togl *togl, const char *filename, int rgbFlag, void (*user_redraw)() )
Generate an encapsulated Postscript file of the image in a Togl widget. filename is the name of the file to generate. If rgbFlag is non-zero then an RGB image file is written, else a grayscale image file is written. user_redraw is a pointer to the function which will render the desired image. This will typically be the same as the function passed to Togl_DisplayFunc().

Tcl Togl commands

These are the Togl commands one may call from a Tcl program.

togl pathName [options]
Creates a new togl widget with name pathName and an optional list of configuration options. Options include: 

Option		Default	Comments
---------------	------- ------------------------------------------------
-width		400	Width of widget in pixels.
-height		400	Height of widget in pixels.

-ident		""	A user identification string ignored by togl.
			This can be useful in your C callback functions
			to determine which Togl widget is the caller.

-rgba		true	If true, use RGB(A) mode
			If false, use Color Index mode

-double		false	If false, request a single buffered window
			If true, request double buffered window

-depth		false	If true, request a depth buffer

-accum		false	If true, request an accumulation buffer

-alpha		false	If true and -rgba is true, request an alpha
			channel

-stencil	false	If true, request a stencil buffer

-privatecmap	false	Only applicable in color index mode.
			If false, use a shared read-only colormap.
			If true, use a private read/write colormap.

-overlay        false   If true, request overlay planes.

-stereo         false   If true, request a stereo-capable window.

-time           1       Specifies the interval, in milliseconds, for
                        calling the C timer callback function which
                        was registered with Togl_TimerFunc.
pathName configure
Returns all configuration records for the named togl widget.
pathName configure -option
Returns configuration information for the specifed option which may be one of:
-width
Returns the width configuration of the widget in the form:
-width width Width W w
where W is the default width in pixels and w is the current width in pixels
-height
Returns the height configuration of the widget in the form:
-height height Height H h
where H is the default height in pixels and h is the current height in pixels
-extensions
Returns a list of OpenGL extensions available. For example: GL_EXT_polygon_offset GL_EXT_vertex_array
pathName configure -option value
Reconfigure a Togl widget. option may be one of:
-width
Resize the widget to value pixels wide
-height
Resize the widget to value pixels high
pathName render
Causes the render callback function to be called for pathName.
pathName swapbuffers
Causes front/back buffers to be swapped if in double buffer mode.
pathName makecurrent
Make the widget specified by pathName the current one.

Demo programs

There are four demo programs:

To compile the demos, edit the Makefile to suit your system, then type "make". The stock Makefile is setup for Linux. To run a demo just type "double" or "texture" or "index" or "overlay".


Reporting Bugs

If you find a bug in Togl please report it to both Ben and Brian. When reporting bugs please provide as much information as possible. Also, it's very helpful to us if you can provide an example program which demonstrates the problem.


Version History

Version 1.0 - March, 1996

Version 1.1 (never officially released)

Version 1.2 - November, 1996

Version 1.3 - May 2, 1997

Future plans


Contributors

Several people have contributed new features to Togl. Among them are:

Many others have contributed bug fixes. Thanks for your contributions!

Last edited on May 2, 1997 by Brian Paul.