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; * src/image.c: Minor copyedits of native transform commentary.

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Eli Zaretskii 2019-06-23 19:24:32 +03:00
parent d2bbea23fa
commit a1deb6cac3
1 changed files with 5 additions and 5 deletions
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src/image.c
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@ -1986,7 +1986,7 @@ compute_image_size (size_t width, size_t height,
Transforms are done by creating a matrix for each action we wish to
take, then multiplying the transformation matrix by each of those
matrices in order (matrix multiplication is not commutative).
After we’ve done that we can use our modified transformation matrix
After we've done that we can use our modified transformation matrix
to transform points. We take the x and y coordinates and convert
them into a 3x1 matrix and multiply that by the transformation
matrix and it gives us a new, transformed, set of coordinates:
@ -1995,7 +1995,7 @@ compute_image_size (size_t width, size_t height,
[m21 m22 ty] X [y] = [m21*x+m22*y+ty*1] = [y']
[ 0 0 1] [1] [ 0*x+0*y+1*1] [ 1]
We don’t have to worry about the last step as the graphics toolkit
We don't have to worry about the last step as the graphics toolkit
will do it for us.
The three transforms we are concerned with are translation, scaling
@ -2029,19 +2029,19 @@ compute_image_size (size_t width, size_t height,
[ 0 0 1]
Where r is the angle of rotation required. Rotation occurs around
the origin, not the centre of the image. Note that this is
the origin, not the center of the image. Note that this is
normally considered a counter-clockwise rotation, however because
our y axis is reversed, (0, 0) at the top left, it works as a
clockwise rotation.
The full process of rotating an image is to move the origin to the
centre of the image (width/2, height/2), perform the rotation, and
center of the image (width/2, height/2), perform the rotation, and
finally move the origin back to the top left of the image, which
may now be a different corner.
Cropping is easier as we just move the origin to the top left of
where we want to crop and set the width and height accordingly.
The matrices don’t know anything about width and height.
The matrices don't know anything about width and height.
It's possible to pre-calculate the matrix multiplications and just
generate one transform matrix that will do everything we need in a