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Tcl/Tk module T219
Drawing on Canvases
Exercises, examples and other material relating to training module T219. This topic is presented on public courses Learning to program in Tcl, Tcl/Tk, 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 subjectupdated
4460Using 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] Station ...
2211Tcl/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
Using a Tcl/Tk canvas
Background information
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.
Canvas and Canvas objects.
Interacting with drawing objects.
Canvas objects.
The rectangle (rect) object.
The oval object.
The polygon object.
The arc object.
The line object.
The text object.
Computer graphics - techniques.
Coordinate systems.
Display lists.
Hidden line and surface.
Further issues.
Complete learning
If you are looking for a complete course and not just a information on a single subject, visit our Listing and schedule page.

Well House Consultants specialise in training courses in Tcl/Tk, Expect,Ruby, Lua, Python, Perl, PHP, and MySQL. We run Private Courses throughout the UK (and beyond for longer courses), and Public Courses at our training centre in Melksham, Wiltshire, England. It's surprisingly cost effective to come on our public courses - even if you live in a different country or continent to us.

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