Exercises, examples and other material relating to training module T219. This topic is presented on public courses Learning to program in Tcl
, Tcl Programming
Tcl/Tk GUIs consist largely of components such as buttons, labels entry boxes and sliders. Sometimes you'll need something that's much more graphic and for this you'll use a canvas widget. You can write to a canvas down to individual pixel level, and you can also draw lines, ovals, rectangles, text and polygons. This module studies the options for drawing to and manipulating a canvas, and introduces computer graphic techniques such as world to pixel co-ordinate transformations and display list manipulation.
|Articles and tips on this subject||updated|
|4460||Using Object Oriented Tcl and the Tk toolkit together - real life example|
There are all sorts of ways to look at the survey data we gathered last October on the TransWilts trains, and one fact I'm particularly interested in is the journey lengths of passengers. I have all the information to hand that I need to work this out - but in different files:
Survey data [here]
|2211||Tcl/Tk - why does the canvas widget use a display list?|
"Tcl/Tk uses a display list when you draw on a canvas widget." OK - so what does that really mean?
With most of the languages that we teach, any graphics you draw go straight into a frame buffer of a memory map that represents a frame buffer, so the earlier elements added to your graphic will be destructively ...
Examples from our training material
|can1|| Drawing on a canvas|
|can2|| Drawing shapes on a canvas and dragging them with the mouse|
|can3|| Demo of different graphic objects|
|can4|| Line styles on a Tk canvas|
|histo|| Histogram drawn on a canvas - generalised code|
|imgoncanvas.tk|| Placing a GIF on a canvas|
|tktext|| text options in Tk - colour, font, size, centring|
PicturesUsing a Tcl/Tk canvas
Some modules are available for download
as a sample of our material or under an Open Training Notes License
for free download from [here]
Topics covered in this module
Canvas basics; coordinate system, colour, etc.
Canvas objects. Rect, text, line, etc.
Attributes of canvas objects.
The display list, tagging and manipulating objects.
Tips and techniques for graphics programming.
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