http://www710.univ-lyon1.fr/~jciehl/Public/OpenGL_PG/figures/chap3-11.gif
On 18 Giu, 19:42, Paolo <brand...@gmail.com> wrote:
> I have to traslate into the z-axis a bit, otherwise I wouldn't see
> anything on the screen.
>
> Anyway, I'm doing this step by step as you said to me ;)
> At first i traslate the quad to the origin and in fact i see it there.
> Then I rotate of 45 degree around the z-axis and I see it rotated
> right.
>
> At last I traslate it again to the previous position, but the quad
> goes to a different position from that which I expected.
> Instead, if i do after the rotation:
>
> glTraslete(1.0f, 0f,0f);
>
> the quad moves of an unit along x-axis as if also this was rotated of
> 45 degrees, nord-east direction (in order to intend us) and not east-
> direction as I expect. I hope you undestrand me now :(
>
> Paolo
>
> p.s. if you prefer I can post my code
>
> On 18 Giu, 18:45, Leigh McRae <leigh.mc...@lonedwarfgames.com> wrote:
>
>
>
> > I am not exactly sure what you're saying actually. At any rate, I
> > noticed that you're translating along the z-axis. If you're rotating
> > around the z-axis you don't need to translate along z. Also it could be
> > that you're translating the quad offscreen since you haven't mirrored
> > the z translation.
>
> > Anyway, what are you seeing? Did you change the order? I would do it
> > step by step. Start with getting the translation to the origin right.
> > Once that looks right then add the rotation. Finally add the translation
> > back.
>
> > Leigh
>
> > On 6/18/2010 12:35 PM, Paolo wrote:
>
> > > Thanks for your answer.
>
> > > my matrix is GL_MODELVIEW.
> > > I have noticed that once I have traslated and rotated the quad, also
> > > the aces x,y,z seem to be rotated of 45 degree. If it is right, it's
> > > normal that when i applied the second traslalte the quad goes in
> > > another position.
>
> > > is it normal? is there something wrong?
>
> > > On 18 Giu, 18:21, Leigh McRae<leigh.mc...@lonedwarfgames.com> wrote:
>
> > >> OpenGL applies it's transforms in reverse so maybe swap the two
> > >> translates. Sounds lame but this is the sort of thing you get right
> > >> once and don't look at again for sometime. Also make sure your matrix
> > >> mode is GL_MODELVIEW.
>
> > >> Leigh
>
> > >> On 6/18/2010 11:58 AM, Paolo wrote:
>
> > >>> Hi leigh!
> > >>> I've tried, but it doesn't work... the quad goes in a wrong position :
> > >>> (
>
> > >>> My quad has these coordinates
>
> > >>> //vertex bottom left
> > >>> vertex[0] = 9.5f;
> > >>> vertex[1] = 10f;
> > >>> vertex[2] = 0.0f;
> > >>> //top left
> > >>> vertex[3] = 9.5f;
> > >>> vertex[4] = 11.0f;
> > >>> vertex[5] = 0.0f;
> > >>> //bottom right
> > >>> vertex[6] = 10.5f;
> > >>> vertex[7] = 10f;
> > >>> vertex[8] = 0.0f;
> > >>> //top right
> > >>> vertex[9] = 10.5;
> > >>> vertex[10] = 11f;
> > >>> vertex[11] = 0.0f;
>
> > >>> and this is my draw function...
>
> > >>> public void draw(GL10 gl){
> > >>> gl.glPushMatrix();
> > >>> gl.glTranslatef(-10, -10.5f, 0); //to the origin
>
> > >>> gl.glRotatef(45, 0, 0, -1); //rotate
>
> > >>> gl.glTranslatef(10, 10.5f, -2.0f); //back to previous position
>
> > >>> // Enabled the vertices buffer for writing and to be used during
> > >>> // rendering.
> > >>> gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
> > >>> // Specifies the location and data format of an array of vertex
> > >>> // coordinates to use when rendering.
> > >>> gl.glVertexPointer(3, GL10.GL_FLOAT, 0, markerBuffer);
> > >>> gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, NUMERO_VERTICI);
> > >>> // Disable the vertices buffer.
> > >>> gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
> > >>> gl.glPopMatrix();
>
> > >>> }
>
> > >>> On 18 Giu, 17:31, Leigh McRae<leigh.mc...@lonedwarfgames.com> wrote:
>
> > >>>> Translate the quad to the origin, rotate, translate back.
>
> > >>>> Leigh
>
> > >>>> On 6/18/2010 11:12 AM, Paolo wrote:
>
> > >>>>> Hi guys!
> > >>>>> I'm a newbie in OpenGL. :D
> > >>>>> I'm trying to rotate a quad around its center.
>
> > >>>>> This is my scenario: I've a quad, drawn with TRIANGLE_STRIP, at
> > >>>>> specified coordinates. Now I want to rotate of 45 degrees around its
> > >>>>> center, without move it from its position, not around the origin of
> > >>>>> the aces.
> > >>>>> I hope you are able to understand my english... :)
>
> > >>>>> How can I do that?
>
> > >>>>> Thanks
>
> > >>>>> Paolo
>
> > >>>> --
> > >>>> Leigh McRaewww.lonedwarfgames.com
>
> > >> --
> > >> Leigh McRaewww.lonedwarfgames.com
>
> > --
> > Leigh McRaewww.lonedwarfgames.com
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