vpWindow(3)

💖 vpWindow(3) 💖

okay so bestie, welcome to the vpWindow page from the Library Functions Manual — this is the one where we multiply the projection matrix by a perspective or orthographic matrix. it's giving math but make it cute. let's go 🦋

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✨ NAME ✨

vpWindow — multiply the projection matrix by a perspective or orthographic matrix 🎀

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🌸 SYNOPSIS 🌸

#include <volpack.h>

vpResult
vpWindow(vpc, type, left, right, bottom, top, near, far)
    vpContext *vpc;
    int type;
    double left, right;
    double bottom, top;
    double near, far;

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🫶 ARGUMENTS 🫶

• vpc — the VolPack context, and you get it from vpCreateContext. your whole little universe lives in here 💜
• type — the projection type code. right now? it must be VP_PARALLEL. no cap, that's the only option.
• left — the coordinate of the left vertical clipping plane.
• right — the coordinate of the right vertical clipping plane.
• bottom — the coordinate of the bottom horizontal clipping plane.
• top — the coordinate of the top horizontal clipping plane.
• near — the coordinate of the near depth clipping plane.
• far — the coordinate of the far depth clipping plane.

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👑 DESCRIPTION 👑

vpWindow is here to multiply the current projection matrix by a perspective or orthographic projection matrix. iconic behavior honestly ✨

the new projection matrix is defined by the coordinates of six clipping planes, all in the eye coordinate system (peep vpCurrentMatrix(3) for that whole situation 👀). and the way this matrix works? it maps the points (left, bottom, near) and (right, top, near) to the lower left and upper right corners of the clipping window. periodt. 💅

if you want an alternative means of specifying the projection matrix, go look at vpWindowPHIGS(3). choices, we love them 🎀

real talk though: currently, only orthographic projections are supported. perspective projections will be added in a future release. so don't come for me about perspective yet, it's coming, we're manifesting it 🧚

the matrix for parallel projections is:

A   0   0   D
 0   B   0   E
 0   0   C   F
 0   0   0   1

and the pieces are:

A = 2 / (right - left)
B = 2 / (top - bottom)
C = 2 / (far - near)
D = (left + right) / (left - right)
E = (bottom + top) / (bottom - top)
F = (near + far) / (near - far)

so the matrix is multiplied into the projection matrix — and even if the projection matrix is not the current matrix. yes, that's on purpose, it's just how it is 💀

by default, the matrix is post-multiplied (N = N*m where N is the current matrix and m is the argument to vpMultMatrix). if you'd rather pre-multiply, the VP_CONCAT_MODE option to vpSeti can be used to select pre-multiplication. your matrix, your rules 💖

and the default window? it's a parallel projection with left = bottom = near = -0.5, and right = top = far = 0.5. so cozy. so centered. main character energy fr fr 🌈

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⭐ STATE VARIABLES ⭐

the current matrix concatenation parameters can be retrieved with the following state variable codes (see vpGeti(3)):

• VP_CONCAT_MODE

that's the whole list bestie, it's a short one 🫶

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💀 ERRORS 💀

the normal return value is VP_OK. the following error return values are possible:

• VPERROR_BAD_VALUE — the clipping plane coordinates are invalid (left >= right, etc.). yeah. if your left is chillin' to the right of your right, we have a problem 🙈
• VPERROR_BAD_OPTION — the type argument is invalid.

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🔥 SEE ALSO 🔥

VolPack(3), vpCreateContext(3), vpCurrentMatrix(3), vpWindowPHIGS(3)

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and that's the page!! 🎀✨ this little baddie comes to you from VolPack, and yes, she is still vpWindow(3) — slay, go multiply some matrices, ily 💖🦋🌸