Shear camera frustum

num3ric · October 8, 2015, 10:36pm

Is it possible to apply xy lens offsets to a camera, effectively shearing the camera frustum? I fear this functionality is not built in.

num3ric · October 9, 2015, 9:42pm

num3ric · October 9, 2015, 9:49pm

num3ric · October 13, 2015, 3:40pm

Here’s how this is handled in cinder:

github.com

cinder/Cinder/blob/master/src/cinder/Camera.cpp#L310

      
        
            	}
            
            
	if( mLensShift.x != 0.0f ) {
            		mFrustumRight = ci::lerp<float, float>(2.0f * mFrustumRight, 0.0f, 0.5f - 0.5f * mLensShift.x);
            		mFrustumLeft = ci::lerp<float, float>(0.0f, 2.0f * mFrustumLeft, 0.5f - 0.5f * mLensShift.x);
            	}
            
            
	mat4 &p = mProjectionMatrix;
            	p[0][0] =  2.0f * mNearClip / ( mFrustumRight - mFrustumLeft );
            	p[1][0] =  0.0f;
            	p[2][0] =  ( mFrustumRight + mFrustumLeft ) / ( mFrustumRight - mFrustumLeft );
            	p[3][0] =  0.0f;
            
            
	p[0][1] =  0.0f;
            	p[1][1] =  2.0f * mNearClip / ( mFrustumTop - mFrustumBottom );
            	p[2][1] =  ( mFrustumTop + mFrustumBottom ) / ( mFrustumTop - mFrustumBottom );
            	p[3][1] =  0.0f;
            
            
	p[0][2] =  0.0f;
            	p[1][2] =  0.0f;
            	p[2][2] = -( mFarClip + mNearClip ) / ( mFarClip - mNearClip );

num3ric · October 13, 2015, 3:42pm

For now, I am passing lens shift offsets from UCameraComponent all the way down to the FReversedPerspectiveMatrix, like so:

FORCEINLINE FReversedZPerspectiveMatrix::FReversedZPerspectiveMatrix( float HalfFOVX, float HalfFOVY, float MultFOVX, float MultFOVY, float MinZ, float MaxZ, FVector2D shift )
	: FMatrix(
		FPlane( MultFOVX / FMath::Tan( HalfFOVX ), 0.0f, 0.0f, 0.0f ),
		FPlane( 0.0f, MultFOVY / FMath::Tan( HalfFOVY ), 0.0f, 0.0f ),
		FPlane( -shift.X, -shift.Y, ((MinZ == MaxZ) ? 0.0f : MinZ / (MinZ - MaxZ)), 1.0f ),
		FPlane( 0.0f, 0.0f, ((MinZ == MaxZ) ? MinZ : -MaxZ * MinZ / (MinZ - MaxZ)), 0.0f )
		)
{ }

This appears to be working as expected. (Not sure why the signs have to be flipped.) The debug draw frustums are unchanged however. This may require further modifications.

anonymous_user_12c704cc · July 16, 2018, 3:09am

Thank you for providing such a solution.
Can you be more specific in UCameraComponent detail how to change it? Thank you~

OOOllieML · July 5, 2024, 1:38pm

When using this, it appears as if my camera is rotated at the same time and doesn’t correctly line up with the shift I am applying?