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minor typo fix: It you want -> If you want #63

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minor typo fix: It you want -> If you want #63

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4 changes: 2 additions & 2 deletions beginners-tutorials/tutorial-3-matrices/index.markdown
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Expand Up @@ -237,7 +237,7 @@ Let's quote Futurama again :

![]({{site.baseurl}}/assets/images/tuto-3-matrix/camera.png)

When you think about it, the same applies to cameras. It you want to view a moutain from another angle, you can either move the camera... or move the mountain. While not practical in real life, this is really simple and handy in Computer Graphics.
When you think about it, the same applies to cameras. If you want to view a moutain from another angle, you can either move the camera... or move the mountain. While not practical in real life, this is really simple and handy in Computer Graphics.

So initially your camera is at the origin of the World Space. In order to move the world, you simply introduce another matrix. Let's say you want to move your camera of 3 units to the right (+X). This is equivalent to moving your whole world (meshes included) 3 units to the LEFT ! (-X). While you brain melts, let's do it :

Expand Down Expand Up @@ -396,4 +396,4 @@ In tutorial 6 you'll learn how to modify these values dynamically using the keyb

_Addendum_

[^projection]: [...]luckily for us, a 4x4 matrix can represent this projection : Actually, this is not correct. A perspective transformation is not affine, and as such, can't be represented entirely by a matrix. After beeing multiplied by the ProjectionMatrix, homogeneous coordinates are divided by their own W component. This W component happens to be -Z (because the projection matrix has been crafted this way). This way, points that are far away from the origin are divided by a big Z; their X and Y coordinates become smaller; points become more close to each other, objects seem smaller; and this is what gives the perspective. This transformation is done in hardware, and is not visible in the shader.
[^projection]: [...]luckily for us, a 4x4 matrix can represent this projection : Actually, this is not correct. A perspective transformation is not affine, and as such, can't be represented entirely by a matrix. After beeing multiplied by the ProjectionMatrix, homogeneous coordinates are divided by their own W component. This W component happens to be -Z (because the projection matrix has been crafted this way). This way, points that are far away from the origin are divided by a big Z; their X and Y coordinates become smaller; points become more close to each other, objects seem smaller; and this is what gives the perspective. This transformation is done in hardware, and is not visible in the shader.