glBomb

02-13-2007, 04:59 AM

http://img184.imageshack.us/img184/9649/upld2cm4.png (http://imageshack.us)

Hi people

I tried to draw a simple quad from (-3,-4) to (0,0) using the commands below:

glBegin();

glVertex2i(-3,-4);//Top left

glVertex2i(0,-4);//Top right

glVertex2i(0,0);//Bottom right

glVertex2i(-3,0);//Bottom left

glEnd();

and i got the output in the left picture.The blue pixel is the origin.The yellow pixels are the pixels where i expected the quad boundary to be.And the red pixels are the actual output.What i cant get is if i want the upper left corner of the quad at(-3,-4) why is it ending up at (-3,-3)?

Also the bottom is not at the origin.there is a problem with the y-direction here

Then i tried positive numbers as:

glBegin();

glVertex2i(0,0);//Top left

glVertex2i(0,3);//Top right

glVertex2i(3,4);//Bottom right

glVertex2i(0,4);//Bottom left

glEnd();

Now i get the output at the right.Now there is a problem with the x-direction !!

Is there some convention regarding the drawing of quads in opengl ? That the boundary pixels will not be drawn?

Thanks...

Hi people

I tried to draw a simple quad from (-3,-4) to (0,0) using the commands below:

glBegin();

glVertex2i(-3,-4);//Top left

glVertex2i(0,-4);//Top right

glVertex2i(0,0);//Bottom right

glVertex2i(-3,0);//Bottom left

glEnd();

and i got the output in the left picture.The blue pixel is the origin.The yellow pixels are the pixels where i expected the quad boundary to be.And the red pixels are the actual output.What i cant get is if i want the upper left corner of the quad at(-3,-4) why is it ending up at (-3,-3)?

Also the bottom is not at the origin.there is a problem with the y-direction here

Then i tried positive numbers as:

glBegin();

glVertex2i(0,0);//Top left

glVertex2i(0,3);//Top right

glVertex2i(3,4);//Bottom right

glVertex2i(0,4);//Bottom left

glEnd();

Now i get the output at the right.Now there is a problem with the x-direction !!

Is there some convention regarding the drawing of quads in opengl ? That the boundary pixels will not be drawn?

Thanks...