Hmm ok.. I think I may have overlooked a key piece of data here.. namely the structure of the matrix being rotated.
I use a simple grid to represent most of my 2D shapes, but I assign the coordinates of the grid such that when it is positioned at 0,0 it is the center of the grid that is at these coordinates. This means I don't need to translate to the half-values you mention. I'm guessing that your grid (matrix) has all positive values for its coordinates, whereas I have half the values as negatives which means my grid is already "center aligned". You may want to try the same as it will save the extra GL calls and if you have a lot of objects this could become meaningful. On Nov 4, 12:37 am, "Alistair." <[email protected]> wrote: > Thanks Jason. One month later and I finally got it working. You were > correct but it has taken a bit of time me to get my head around what > was going on. You suggestion wouldrotatethe texture around the point > at which it was drawn but I wanted torotateit around it's mid-point. > I see now that the secret is to: > > - translate the origin to a draw point plus half the width and height. > -rotate > - translate back by half the width and height. > - draw > > Here is my code. Note to anyone looking at this that I have just tried > it out and I am sure it can be tidied up. Also most importantly I am > adjusting the co-ordinate system to match that of canvas where the top > left is (0,0). This is because by drawing primitives as set to work in > Canvas as well. > > surface.glMatrixMode(GL10.GL_MODELVIEW); > > Grid.beginDrawing(surface, true, false); > > surface.glBindTexture(GL10.GL_TEXTURE_2D, ids[index]); > > surface.glLoadIdentity(); > > surface.glPushMatrix(); > > // Draw using the DrawTexture extension. > float drawWidth = texture.getDrawWidth(); > float drawHeight = texture.getDrawHeight(); > float ypos = screenHeight - drawHeight - y; > > if (angle>0) > { > float halfWidth = drawWidth/2; > float halfHeight = drawHeight/2; > > surface.glTranslatef(x+halfWidth, ypos+halfHeight, 0); > > surface.glRotatef(-angle, 0.0f, 0.0f, 1.0f); > > surface.glTranslatef(-halfWidth, -halfHeight, 0); > } > else > { > surface.glTranslatef(x, ypos, 0); > } > > texture.getGrid().draw(surface, true, true); > > surface.glPopMatrix(); > > Grid.endDrawing(surface); > > surface.glDisable(GL10.GL_TEXTURE_2D); > > Al. > > On Oct 15, 3:37 pm, Jason <[email protected]> wrote: > > > > > > > > > You want to call glLoadIdentity before anything else, and remember > > that the commands are on a stack, so are processed in "reverse" order. > > > The glLoadIdentity will reset everything, so your matrix will be at > > 0,0. This means you draw,rotate, then translate; but you push the > > commands to do this onto the stack in reverse order. > > > Here's what I do: > > > // Load the identity matrix so we always start from 0,0 > > gl.glLoadIdentity(); > > > // push a copy of the matrix on the stack to manipulate > > gl.glPushMatrix(); > > > // translate to target coordinates. > > gl.glTranslatef(x, y, 0.0f); > > > // Scale if needed > > // gl.glScalef(scaleX, scaleY, 1.0f); > > > //Rotate(must be in degrees) > > gl.glRotatef((float)Math.toDegrees(angle), 0, 0, 1.0f); > > > // push the draw command last > > grid.draw(gl); > > > // finally pop the matrix > > gl.glPopMatrix(); > > > There is NO need to re-translate back anywhere.. and certainly no need > > to perform an additional rotation as suggested. > > > On Oct 15, 8:42šam, Kostya Vasilyev <[email protected]> wrote: > > > > Add anotherrotatecall before the non-working translate, with the inverse > > > angle (in your case, the value in 'angle' without the '-'). > > > > This will reverse the rotation so the translate call can undo the > > > translation. > > > > -- > > > Kostya Vasilyev --http://kmansoft.wordpress.com > > > > 15.10.2010 1:30 ÐÏÌØÚÏ×ÁÔÅÌØ "Alistair." <[email protected]> > > > ÎÁÐÉÓÁÌ: > > > > Alas, that had no effect. I have _something_ sort of working > > > > š š š š š šsurface.glMatrixMode(GL10.GL_MODELVIEW); > > > > surface.glEnable(GL10.GL_TEXTURE_2D); > > > > surface.glBindTexture(GL10.GL_TEXTUR... > > > š š š š š šGrid.beginDrawing(surface, true, false); > > > > š š š š š šsurface.glPushMatrix(); > > > > // Draw using the DrawTexture extension. > > > š š š š š šint drawHeight = texture.getDrawHeight(); > > > š š š š š šint drawWidth = texture.getDrawWidth(); > > > š š š š š šfloat ypos = screenHeight - drawHeight- y; > > > > š š š š š šsurface.glLoadIdentity(); > > > > š š š š š šsurface.glTranslatef(x, ypos, 0); > > > > surface.glRotatef(-angle, 0.0f, 0.0f, 1.0f); > > > š š š š š šsurface.glTranslatef(-x, -ypos, 0); // THIS NOT DOING WHAT > > > I THOUGHT WOULD > > > > š š š š š štexture.getGrid().draw(surface, true, false); > > > > š š š š š šsurface.glPopMatrix(); > > > > š š š š š šGrid.endDrawing(surface); > > > > surface.glDisable(GL10.GL_TEXTURE_2D); > > > What I can't seem to get working now it the re-translate back to the > > > original point after the rotation. > > > > On Oct 12, 6:02 am, Kunal Kant <[email protected]> wrote: > > > > > remove that line " surface.glLoad... > > > > <[email protected]>wrote: > > > > > > I am trying torotateabitmapinOpenGL. I have searched around and > > > > > come up w... > > > > > [email protected]<android-developers%2Bunsubs > > > > > [email protected]><android-developers%2Bunsubs > > > > [email protected]> > > > > > > For more options, visit this group at > > > > >http://groups.google.com/group/android-developers?hl=en... -- 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
