Drawing in absolute pixels
Author
Hi, can I draw a quad by defining the pixels for the vertices instead of scaled opengl coordinates?
thx
Sure. It's easy.
Premature optimizations can only slow down your project even more.
Edited by - tangentz on February 16, 2002 3:27:01 PM
// Set the size of the view portglViewport(0, 0, Width, Height);// Use orthographica projectionglMatrixMode(GL_PROJECTION);glLoadIdentity(); // Edit: Forgot to add thisglOrtho(0, Width, Height, 0, 0, 1);// Render the objectsglMatrixMode(GL_MODELVIEW);glLoadIdentity();// Now you can draw stuff in pixel coordinates.// The upper left is (0, 0)// The lower right is (Width, Height) Premature optimizations can only slow down your project even more.
Edited by - tangentz on February 16, 2002 3:27:01 PM
Author
Thank you but your answer only works to 50%. I want a rectangle which is 50 pixels wide and 768 pixels long. It's supposed to cover the left side of the monitor (as part of an GUI). The code I used is:
The rectangle is drawn perfectly, but the scene is translated 128 pixels right, and the rectangle is only 37 pixels wide. Why???
Edited by - Peaceman on February 16, 2002 1:34:03 PM
glPushMatrix(); glViewport(0, 0, WindowWidth, WindowHeight); // Set the size of the view port glMatrixMode(GL_PROJECTION); // Use orthographica projection glOrtho(0, WindowWidth, WindowHeight, 0, 0, 1); // Render the objects glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glColor4f(1.0f, 0.0f, 1.0f, 1.0f); glBegin(GL_QUADS); { glVertex3f(0.0f , 0.0f, 0.0f); glVertex3f(0.0f ,767.0f, 0.0f); glVertex3f(50.0f,767.0f, 0.0f); glVertex3f(50.0f, 0.0f, 0.0f); } glEnd(); glPopMatrix(); The rectangle is drawn perfectly, but the scene is translated 128 pixels right, and the rectangle is only 37 pixels wide. Why???
Edited by - Peaceman on February 16, 2002 1:34:03 PM
Put a glLoadIdentity(); between glMatrixMode(GL_PROJECTION); and glOrtho(0, WindowWidth, WindowHeight, 0, 0, 1);
glOrtho, gluOrtho2D, gluPerspective, etc. are all matrix MULTIPLICATIONS. So if you want to replace the current matrix you should call glLoadIdentity first.
Also, it's probably better to change your glOrtho statement into this: glOrtho(0, WindowWidth, WindowHeight, 0, -1, 1); or this: glOrtho(0, WindowWidth, 0, WindowHeight, -1, 1);
Because otherwise drawing at depth 0 draws exactly at the near clipping plane. It's safer to draw between the near and far clipping planes.
Edited by - Scarab0 on February 16, 2002 3:09:26 PM
glOrtho, gluOrtho2D, gluPerspective, etc. are all matrix MULTIPLICATIONS. So if you want to replace the current matrix you should call glLoadIdentity first.
Also, it's probably better to change your glOrtho statement into this: glOrtho(0, WindowWidth, WindowHeight, 0, -1, 1); or this: glOrtho(0, WindowWidth, 0, WindowHeight, -1, 1);
Because otherwise drawing at depth 0 draws exactly at the near clipping plane. It's safer to draw between the near and far clipping planes.
Edited by - Scarab0 on February 16, 2002 3:09:26 PM
quote:Original post by Peaceman
Thank you, it works fine now, but why is a near clipping value of 0 a bad idea?
Well it''s not really a bad idea in Ortho mode. In fact it should always work if you''re drawing at depth 0.
-1 is just safer because 0 is definately between -1 and 1, with 0 and 1 it''s not that clear.
So maybe it''s just paranoid of me, but I prefer [-1, 1].
BTW, another tip: you can just use:
glVertex2f(0.0f , 0.0f); instead of glVertex3f because glVertex2f is equivalent to calling glVertex3f with a Z of 0. It''s shorter so maybe it''ll save you some time.
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