[Task] Optimize trigonometry out of MapblockMeshGenerator::drawLiquidTop

[numberZero]

minetest/src/client/content_mapblock.cpp

Lines 665 to 675 in 2a8becd

	f32 tcoord_angle = atan2(dz, dx) * core::RADTODEG;
	v2f tcoord_center(0.5, 0.5);
	v2f tcoord_translate(blockpos_nodes.Z + p.Z, blockpos_nodes.X + p.X);
	tcoord_translate.rotateBy(tcoord_angle);
	tcoord_translate.X -= floor(tcoord_translate.X);
	tcoord_translate.Y -= floor(tcoord_translate.Y);
	for (video::S3DVertex &vertex : vertices) {
	vertex.TCoords.rotateBy(tcoord_angle, tcoord_center);
	vertex.TCoords += tcoord_translate;
	}

Using atan2, sin, and cos (in rotateBy) is not necessary for rotation as $\frac{\sin(\mathrm{atan2}(y, x))}{\cos(\mathrm{atan2}(y, x))} = \frac{y}{x}$.

[arihant2math]

https://github.com/minetest/irrlicht/blob/cd3e7845344a413a73d2649e3e99d51f14eb12fb/include/vector2d.h#L178

Where does the division happen?

[numberZero]

Where does the division happen?

It doesn’t. It’s just an equation that holds.

[numberZero]

Basically, treat atan2 arguments as a vector, normalize it, and you get sine and cosine of the angle atan2 would return. Watch out for signs though.

[numberZero]

5276c16