Orthographic Projection Issue

Whether you're a newbie or an experienced programmer, any questions, help, or just talk of any language will be welcomed here.

Moderator: Coders of Rage

Post Reply
nickyc95
Chaos Rift Newbie
Chaos Rift Newbie
Posts: 9
Joined: Wed Mar 05, 2014 11:12 am

Orthographic Projection Issue

Post by nickyc95 »

I have a problem with my Ortho Matrix. The engine uses the perspective projection fine but for some reason the Ortho matrix is messed up. (See screenshots below).

Can anyone understand what is happening here?

At the min I am taking the Projection matrix * Transform (Translate, rotate, scale) and passing to the Vertex shader to multiply the Vertices by it.

void Matrix4f::InitOrthoProjTransform(float left, float right, float top, float bottom, float zNear, float zFar)
{
    m[0][0] = 2 / (right - left);   
    m[0][1] = 0;                        
    m[0][2] = 0;                        
    m[0][3] = 0;

    m[1][0] = 0;                        
    m[1][1] = 2 / (top - bottom);   
    m[1][2] = 0;                        
    m[1][3] = 0;

    m[2][0] = 0;                        
    m[2][1] = 0;                        
    m[2][2] = -1 / (zFar - zNear);  
    m[2][3] = 0;

    m[3][0] = -(right + left) / (right - left);
    m[3][1] = -(top + bottom) / (top - bottom);
    m[3][2] = -zNear / (zFar - zNear);
    m[3][3] = 1;
}
This image shows the Perspective projection:
Persp
Persp
2Untitled-1.png (12.12 KiB) Viewed 2334 times
Then the Orthographic projection (InitOrthoProjectionTransform(0.0f, 800.0f, 0.0f, 600.0f, 0.1f, 1000.0f) )
(I'll upload a video to demonstrate what is happening.)
Ortho
Ortho
1Untitled-1.png (14.67 KiB) Viewed 2334 times

VIDEO Shows the same scene, rotating on the Y axis.
http://youtu.be/2feiZAIM9Y0
X Abstract X
Chaos Rift Regular
Chaos Rift Regular
Posts: 173
Joined: Thu Feb 11, 2010 9:46 pm

Re: Orthographic Projection Issue

Post by X Abstract X »

Try these 2 changes:
void Matrix4f::InitOrthoProjTransform(float left, float right, float top, float bottom, float zNear, float zFar)
{
    m[0][0] = 2 / (right - left);   
    m[0][1] = 0;                        
    m[0][2] = 0;                        
    m[0][3] = 0;

    m[1][0] = 0;                        
    m[1][1] = 2 / (top - bottom);   
    m[1][2] = 0;                        
    m[1][3] = 0;

    m[2][0] = 0;                        
    m[2][1] = 0;                        
    m[2][2] = -2 / (zFar - zNear);  
    m[2][3] = 0;

    m[3][0] = -(right + left) / (right - left);
    m[3][1] = -(top + bottom) / (top - bottom);
    m[3][2] = -(zFar + zNear) / (zFar - zNear);
    m[3][3] = 1;
}
nickyc95
Chaos Rift Newbie
Chaos Rift Newbie
Posts: 9
Joined: Wed Mar 05, 2014 11:12 am

Re: Orthographic Projection Issue

Post by nickyc95 »

X Abstract X wrote:Try these 2 changes:
void Matrix4f::InitOrthoProjTransform(float left, float right, float top, float bottom, float zNear, float zFar)
{
    m[0][0] = 2 / (right - left);   
    m[0][1] = 0;                        
    m[0][2] = 0;                        
    m[0][3] = 0;

    m[1][0] = 0;                        
    m[1][1] = 2 / (top - bottom);   
    m[1][2] = 0;                        
    m[1][3] = 0;

    m[2][0] = 0;                        
    m[2][1] = 0;                        
    m[2][2] = -2 / (zFar - zNear);  
    m[2][3] = 0;

    m[3][0] = -(right + left) / (right - left);
    m[3][1] = -(top + bottom) / (top - bottom);
    m[3][2] = -(zFar + zNear) / (zFar - zNear);
    m[3][3] = 1;
}
Hi, thanks for the reply.

Changing the ortho matrix to the one you have posted still hasn't fixed the issue.

Thanks
X Abstract X
Chaos Rift Regular
Chaos Rift Regular
Posts: 173
Joined: Thu Feb 11, 2010 9:46 pm

Re: Orthographic Projection Issue

Post by X Abstract X »

What are the results if you omit using any model or camera transforms and multiply the vertices of an on-screen quad by just the ortho matrix?
nickyc95
Chaos Rift Newbie
Chaos Rift Newbie
Posts: 9
Joined: Wed Mar 05, 2014 11:12 am

Re: Orthographic Projection Issue

Post by nickyc95 »

X Abstract X wrote:What are the results if you omit using any model or camera transforms and multiply the vertices of an on-screen quad by just the ortho matrix?
Hi there,

Turns out my math class isn't pristine :lol:

I was swapping conventions from the actual math class and the orthographic matrix.

I just have to ensure I am more constant with the conventions that I use.

Thank you :)
Post Reply