[Qt-interest] How to draw a 2-D matrix as a 3-D surface

[Fabio Giovagnini]

All true.
But I'm not so familiar with withgets building.
I thinmk that the best solution is to add
http://qwtplot3d.sourceforge.net/
to my project and use its approach that is exactly what I need.

Thanks for your raodmap for sure usefull to get customization of existing  
stuff.

Thanks lot.
I'm more familiar with embedded devices and related software, so for the 
software runnung on PC generally I limit my action to collect existing 
features.

Thanks again


Alle 11:10, lunedì 20 aprile 2009, Oliver.Knoll at comit.ch ha scritto:
> Fabio Giovagnini wrote on Monday, April 20, 2009 10:37 AM:
> > I'd like to draw a graph like the attached without usig open GL and
> > without writing tons of code of course. Thanks a lot
>
> Hmmm, to be honest, personally the OpenGL approach would be the easiest
> here ;) The advantage is that you don't need to worry about 3D -> 2D
> transformations, because that's what OpenGL is good at (and was designed
> for in the first place ;)
>
> Here is a rough outline:
>
> - Derive your custom widget from a QGLWidget
> - in the initializeGL() method, setup the GL clear colour, shading model
> (GL_FLAT, for example)
> http://doc.trolltech.com/4.5/opengl-hellogl.html#opengl-initialization - in
> the resizeGL() setup an "ortographic perspective" (use google to get
> example code, checkout the Qt examples)
> http://doc.trolltech.com/4.5/opengl-hellogl.html#resizing-the-viewport sets
> up an "orthographic" view, just as the one you displayed in your screenshot
> and
> - set a fixed camera position which looks at your "elevation field" (the
> graph) (you could easily add rotation, zoom etc. later on) - in the
> paintGL() method, Iterate over all your points in your graph, try to center
> your graph at 0/0/0 (and your camera direction should point to that origin
> as well ;) * x/y are the node coordinates, z is the elevation
>   * use GL_LINE_STRIP, for example, rendering each line in x-direction,
> then each line in y-direction * as z-coordinate your graph value
> ("elevation") of the node in x/y is used * also refer to
> http://doc.trolltech.com/4.5/opengl-hellogl.html#painting-the-scene, for
> example - GL functions you are likely to use (for painting)
>   * glColor
>   * glVertex
>   * glBegin, glEnd
> - Depending on your units in z-direction you might want to add some
> scale-factor as well (so you actually see the elevations better). -
> http://doc.trolltech.com/4.5/qglwidget.html#renderText is useful to draw
> axis labels (the axis you also draw with GL_LINE
>
> Check out the Qt examples on how to setup the camera, perspective,
> background colour etc. For the actual painting I would expect about roughly
> 50 lines of code
>
> Setup is done in GLWidget#initializeGL(), painting is done in
> GLWidget#paintGL(), setup the perspective ("orthographic" or "perspective")
> is done in GLWidget#resizeGL().
>
> Checkout (in german) http://wiki.delphigl.com/index.php/GlBegin for "modes"
> (GL_LINE, GL_LINE_STRIP, GL_TRIANGLE, ...) description, nice illustrations
> :)
>
> Also checkout http://nehe.gamedev.net/lesson.asp?index=01 (you can skip the
> "setup OpenGL on [platform] tutorials - Qt does all that for you ;) For
> example start with
> http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=02 - and hey, "Nehe"
> also provides Qt examples, at the bottom of each tutorial :)
>
> And remember, don't get addicted to the simplicity and elegance of OpenGL
> ;) (once you get the hang with all this "vector and matrix stuff" ;) And
> don't worry: if you (don't) see "a black cube in front of a black
> background with no light, and the camera pointing to the other end of the
> universe..." well, that's one of the very first lessons every OpenGL (3D
> programmers in general) went through ;)
>
>
> Good luck, Oliver

-- 
Fabio Giovagnini

Aurion s.r.l.
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