Mode 7 help

[Kannagi]

So much for the super nes I still have just a study mode 7 and sound.
In mode 7, I know use but does not include calculations to do.
I can possibly copy source code but without understanding I could not use (or source code easy for me to make rotations).
I know that:
|X2 | = | A B | X1 - X0 | + | X0 |
|Y2 | = | C D | Y1 - Y0 | + | Y0 |
A = cos theta
B = sin theta
C = -sin theta
D = cos theta

I find it difficult, any help is welcome.
thank you.

[Sik]

• Imagine a line of length 1 at the angle you want
• "sin theta" is the sine of that value
• "cos theta" is the cosine of that value
• Multiply those two by the amount of scaling you want*

Look up how sine and cosine work related to angles (in short: sine is the vertical distance, cosine is the horizontal distance). Also mind you, just use a look-up table with all the possible angles, the CPU is too weak to calculate it in real time.

*Not sure, may be divide. Either way, you'd figure it out because if it's wrong it'll scale the other way.

[Kannagi]

OK thank you, I'll test.

[Kannagi]

I can more or less do rotation.
and I have a result:


How to do this:
(I scale Y but it does not work).

[lidnariq]

A perspective transformation like that will require the use of HDMA to change the matrix transformation registers on every scanline.

[ccovell]

And also colour addition in HDMA to make it brighter near the horizon.

[Sik]

I don't think he's asking about the fog.

But yeah, the matrix needs to be changed every line. The background is scaled small near the horizon and scaled big near the bottom.

[Kannagi]

But yeah, the matrix needs to be changed every line. The background is scaled small near the horizon and scaled big near the bottom.

Right, I did not understand how he could do this effect.

Thank you, I'll have to work on the HDMA.