[Interest] About the coordinator between the texture and vertex in opengl

[song.7.liu at nokia.com]

Hi,

Sorry that I am still not understand it clearly, let’s begin with follow example:

If I have a vertex array as bellow:

GLint vert[4 * 3]    = {
        -1,  1, 0,
        -1, -1, 0,
        1,  1, 0,
        1, -1, 0 };

And a rectangle will be drawn by:

glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FIXED, 0, vert);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

And if I want to bind a texture to this object without rotation, so how to decide the coordinator of the texture ?

Thanks,
Song

From: interest-bounces+song.7.liu=nokia.com at qt-project.org [mailto:interest-bounces+song.7.liu=nokia.com at qt-project.org] On Behalf Of ext Till Oliver Knoll
Sent: Saturday, December 29, 2012 10:09 PM
To: Qt Project
Subject: Re: [Interest] About the coordinator between the texture and vertex in opengl



Am 29.12.2012 um 12:52 schrieb <song.7.liu at nokia.com<mailto:song.7.liu at nokia.com>>:
...
The problem is about binding a texture to an object, but i am quite not understanding how is the texture coordinator decided according to the vertex coordinator ?

Your question is indeed a little bit off-topic, but your assumption about OpenGL experts here on this list is probably true (disclaimer: it's been quite some while I did some OpenGL code, and that was back when OpenGL 1.4 was current, so "expert" doesn't necessarily include me ;)).

If you haven't done already study this example:

  http://doc.qt.digia.com/qt/opengl-textures.html


specifically


http://doc.qt.digia.com/qt/opengl-textures-glwidget-cpp.html


In GLWidget::makeObject you'll see how for every vertex (world coordinates are usually denoted as X, Y, Z) a corresponding texture coordinate (usually denoted U, V) is specified. That data is then passed on to OpenGL as array with glTexCoordPointer (the "non-OpenGL ES 2 code path") or as array attribute to the GL shader program.


Cheers,
  Oliver




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