CODEWITHSUNDEEP
c++opengl
user2759617
user2759617

Reputation: 707

Drawing a scene in xz plane opengl

I am working on an opengl program. The viewing parameters are : eye 0 -4 6 viewup 0 1 0 lookat 0 0 0

I want to draw a background rectangle (with texture) such that I will be able to see it from the current eye location. Right now, the eye is looking from the -ve Y direction. I want to be able to draw a rectangle that covers the entire screen. I am not understanding what coordinates to give to the rectangle and how to get the texture mapping. Currently I have this in my method: What would be the code for the same. I have this in function:

glPushMatrix();
glLoadIdentity();
glBegin(GL_QUADS);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(-1.0, -1.0);
glVertex2f(-1.0, 1.0);
glVertex2f(1.0, 1.0);
glVertex2f(1.0, -1.0);
glEnd();
glPopMatrix();

Upvotes: 0

Views: 1381

Answers (1)

BDL
BDL

Reputation: 22167

The easiest option for drawing a background image that is independent of the camera is to draw it in normalized device coordinates (NDC) and do not perform any transformations/projections on it. To cover the whole screen, you have to draw a quad going from p = [-1, -1] to [1,1]. The texture coordinates can then be found by tex = (p + 1)/2

Normalized device coordinates are the coordinates one would normally get after applying projection and the perspective divide. They span a cube from [-1,-1,-1] to [1,1,1] where the near plane is mapped to z = -1 (at least in OpenGL, in DirectX the near plane is mapped to z=0). In your special case, the depth should not matter, as long as you draw the background plane as the first element in each frame and disable the depth-test.

Upvotes: 2

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