Look at this image to understand what i'm saying http://www710.univ-lyon1.fr/~jciehl/Public/OpenGL_PG/figures/chap3-11.gif
On 18 Giu, 19:42, Paolo <[email protected]> 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 <[email protected]> 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<[email protected]> 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<[email protected]> 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 -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
