Mini optimization in Raycast

Muchacho · **Joined:** Fri Jan 13, 2012 5:19 pm **Posts:** 1

In the doRaycast() function.
instead of :

Code:

float minx = floorf(x1), maxx = minx + 1.0f;
float tx = ((x1 > x2) ? (x1 - minx) : (maxx - x1)) / std::abs(x2 - x1);
float miny = floorf(y1), maxy = miny + 1.0f;
float ty = ((y1 > y2) ? (y1 - miny) : (maxy - y1)) / std::abs(y2 - y1);
float minz = floorf(z1), maxz = minz + 1.0f;
float tz = ((z1 > z2) ? (z1 - minz) : (maxz - z1)) / std::abs(z2 - z1);

float deltatx = 1.0f / std::abs(x2 - x1);
float deltaty = 1.0f / std::abs(y2 - y1);
float deltatz = 1.0f / std::abs(z2 - z1);

rewrite to :

Code:

float deltatx = 1.0f / std::abs(x2 - x1);
float deltaty = 1.0f / std::abs(y2 - y1);
float deltatz = 1.0f / std::abs(z2 - z1);
   
float minx = floorf(x1), maxx = minx + 1.0f;
float tx = ((x1 > x2) ? (x1 - minx) : (maxx - x1)) * deltatx; //  1.0f / std::abs(x2 - x1)
float miny = floorf(y1), maxy = miny + 1.0f;
float ty = ((y1 > y2) ? (y1 - miny) : (maxy - y1)) * deltaty;
float minz = floorf(z1), maxz = minz + 1.0f;
float tz = ((z1 > z2) ? (z1 - minz) : (maxz - z1)) * deltatz;

Not a bug deal, just less abs call, less subtraction, and overall less divisions.
Sorry I have the "divide desease" for several months. :cry:

Make me feel like Adrian Monk...

David Williams · **Joined:** Sun May 04, 2008 6:35 pm **Posts:** 1827

Thanks for this, I've made the change to Git master. I wouldn't update though as there's a few breaking changes going on at the moment.

The code was based off Christer Ericson's book 'Real Time Collision Detection' so I was naturally curious about why he doesn't make this optimisation. But after looking back at it, it's because he supports traversing over a grid where each cell can be bigger than one (it's for spatial subdivision).

In our case the cell size is always one, which enables the optimisation you suggest.

Mini optimization in Raycast

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