Why MFnCamera.projectionMatrix is different from M3dView.projectionMatrix?

Anonymous · ‎12-09-2020

Hi all,

I want to use my own Projection Matrix, so I make a simple C++ test with Maya2018,

--------------------------------

M3dView ActiveView = M3dView::activeView();

MMatrix viewProjectionMatrix;

ActiveView.projectionMatrix(viewProjectionMatrix);

MDagPath CameraDagPath;

ActiveView.getCamera(CameraDagPath);

MFnCamera Camera(CameraDagPath);

MFloatMatrix CameraProjectionMatrix = Camera.projectionMatrix();

--------------------------------

viewProjectionMatrix is :

[0] 0x000000ed3f9f9e90 {1.9444444444444440, 0.00000000000000000, 5.5512261465384802e-17, 5.5511151231257827e-17}
[1] 0x000000ed3f9f9eb0 {5.3969174808167319e-17, 2.4253565062388596, -2.7756130732692401e-17, -2.7755575615628914e-17}
[2] 0x000000ed3f9f9ed0 {-1.0793834961633464e-16, 6.7317165903770225e-17, -1.0000200002000021, -1.0000000000000000}
[3] 0x000000ed3f9f9ef0 {-4.7896294409778205e-15, -3.4794329937342400e-15, -0.20000200002000021, 0.00000000000000000}

while CameraProjectionMatrix is:

[0] 0x000000ed3f9f9dd0 {1.94444454, 0.000000000, 0.000000000, 0.000000000}
[1] 0x000000ed3f9f9de0 {0.000000000, 3.45679021, 0.000000000, 0.000000000}
[2] 0x000000ed3f9f9df0 {0.000000000, 0.000000000, 1.00001991, -1.00000000}
[3] 0x000000ed3f9f9e00 {0.000000000, 0.000000000, 0.200001985, 0.000000000}

Why the both is different?

viewport width = 933

viewport height=748

FOV = 54.43

Near clipping plane 0.100

Far clipping plane 10000.000

Anonymous · ‎12-14-2020

More tests shows that CameraProjectionMatrix changes with near/far clipping plane, but not with the viewport size,

CameraProjectionMatrix[0][0] and CameraProjectionMatrix[1][1] remain unchanged.

3.45679021 / 1.94444454 = 1920/1080

while 1920*1080 is right my PC's display resolution.

What's happening?

BigRoy · ‎02-10-2021

I think the active view is including the overscan in the projection matrix.

If I disable the Resolution Gate by doing View > Camera Settings > No Gate then the values becomes very similar. Note that this sets the Overscan on the camera to 1.0 on the camera shape.

Here's test code in Python which might be easier to iterate with than in C++:

import maya.api.OpenMaya as om
import maya.api.OpenMayaUI as omui

view = omui.M3dView.active3dView()
view_matrix = view.projectionMatrix()
print view_matrix

sel = om.MSelectionList()
sel.add("persp")
dag = sel.getDagPath(0)
fn_cam = om.MFnCamera(dag)
cam_matrix = fn_cam.projectionMatrix()
print cam_matrix