Re: [PyOpenGL-Users] Missing VBO function

[Roland E. <r.e...@gm...>]

It makes perfectly sens.

Thank you,


Roland.

Le 07/18/10 22:10, Gijs a écrit :
> There certainly won't be any memory leak or corruption. This is the 
> default operation of most, if not all, commands of OpenGL. OpenGL 
> works like a big giant state-machine. You set something, and it'll 
> stay set until you change it or you pop/push states/settings. In your 
> case, a VBO buffer can be bound so that it is made active, and then 
> the commands that use VBO's will use the binded VBO buffer you've set 
> before. If you never unset it, then OpenGL will simply assume that you 
> still want the VBO buffer to be active.
>
> An easier to understand example is when you want to draw a green 
> triangle for instance. If you need to draw a green triangle, and never 
> have to draw a different color, then you can simply set the color to 
> be green before the drawing function. Then call the drawing function, 
> and the color will remain green throughout the entire drawing 
> function. You can call the drawing function again and again, without 
> ever having to set the color to be green. (well, unless you are 
> popping and pushing states which erases states/settings you've set 
> before).
>
> If you understand this concept, you can make quite efficient code, 
> since you know you don't have to call certain functions again and 
> again, simply because they don't (have to) change. And OpenGL usually 
> doesn't change settings for you. There's only one exception to this 
> afaik. When you make an FBO active, it replaces the current settings 
> with the settings of the FBO you made active. Not all of your 
> settings, but the ones that have to do with the colorbuffer and 
> viewport. If you're not sure what settings are set at a certain point 
> in your code, you can get the settings with functions like 
> glGetBooleanv, glGetDoublev, glGetFloatv, glGetIntegerv.
>
> Hope this helps and makes some sense :)
> Kind regards,
> Gijs
>    
>
> On 18-7-2010 19:16, Roland Everaert wrote:
>> Thanks after a few try and error I was able to convert my code to use 
>> that class.
>>
>> I have anyway a question regarding VBO usage in general.
>>
>> What is the effect of not unbinding a VBO buffer after drawing and 
>> calling the drawing process again and again?
>>
>> memory leak?
>>
>> memory corruption?
>>
>> nothing?
>>
>>
>> Thanks,
>>
>>
>> Roland.
>>
>>
>> Le 07/16/10 20:48, Ian Mallett a écrit :
>>> That /was/ a complete example of how to use the functions :-)
>>>
>>> Here, I've added enough surrounding code to be self-explanatory.
>>>
>>> #Import it:
>>> from OpenGL.arrays import vbo
>>> import numpy as np
>>> ...
>>> #Create a vertex buffer object
>>> vertices = [  [0,0,0],[0,1,0],[1,0,0],  [2,0,0],[0,3,0],[4,9,6],  
>>> [7,8,1],...]
>>> vertex_buffer_object = 
>>> vbo.VBO(np.array(vertices,"f"),usage='GL_STATIC_DRAW')
>>> ...
>>> #Draw VBO
>>> glEnableClientState(GL_VERTEX_ARRAY); 
>>> glVertexPointerf(vertex_buffer_object)
>>> glDrawArrays(GL_TRIANGLES,0,len(vertices)/3)
>>> glDisableClientState(GL_VERTEX_ARRAY);
>>> glBindBuffer(GL_ARRAY_BUFFER,0)
>>>
>>> Normal, and texture VBOs work very similarly.  Vertex attribute VBOs 
>>> require you to specify a shader, but you'll only need those for 
>>> things like normal mapping, etc.
>>>
>>> If you need more explanation, try: 
>>> http://pyopengl.sourceforge.net/context/tutorials/shader_1.xhtml, or 
>>> Google: "from OpenGL.arrays import vbo".  My implementation is here: 
>>> http://www.pygame.org/project-glLib+Reloaded-1326-.html, in 
>>> glLib/glLibObjects.py (class glLibObject) but it's probably too 
>>> convoluted for a tutorial.
>>>
>>> Ian
>>
>>
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