Ludum Dare 23: Tiny World

I'm taking part in Ludum Dare this weekend. The theme is Tiny World. Here's what I've managed so far:

This represents about two hours worth of work so far. Most of that time I've spent brainstorming because I was a bit stumped by the theme, but I've got a few ideas now and I'm forging ahead. Wish me luck.

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How to outperform std::vector in 1 easy step

Everyone who's familiar with C++ knows that you should avoid resizing a std::vector inside a loop wherever possible. The reasoning's pretty obvious: the memory allocated for the vector doubles in size each time it fills up and that doubling is a costly operation. Have you ever wondered why it's so costly though?

It's tempting to assume that because implementations of the STL have been around for so long that they must be pretty efficient. It turns out that's a bad assumption because the problem, in this case, is the standard itself: specifically, the allocator interface.

The allocator interface provides two methods that obtain and release memory:

allocate allocates uninitialized storage
(public member function)deallocate deallocates storage
(public member function)

(taken from this page).

What's missing is away of growing an existing memory allocation in place. In C this is provided by the realloc function, but there's no equivalent in the std::allocator interfa…

OpenGL ES and occlusion queries

This is a follow-up to my earlier post "WebGL doesn't have query objects".

Since I wrote that post, the situation has changed a bit. It's still true to say that WebGL doesn't have query objects, but the underlying reason - that OpenGL ES doesn't - is no longer true.

For OpenGL ES 2.0, there's an extension which provides basic query functionality: EXT_occlusion_query_boolean (which seems to have been based on ARB_occlusion_query2 from regular OpenGL). For OpenGL ES 3.0, the functionality from that extension appears to have been adopted into the standard. The extension provides two query types, both of which set a boolean value to indicate whether any pixels passed the depth and stencil tests.

While this is progress, unfortunately it's still not sufficient to implement the pixel accurate collision detection method I described in an earlier post. For that purpose it's not enough to know whether any pixels passed the tests; you want to know whether al…

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WebGL doesn't have query objects.

April 20, 2012

WebGL doesn't support query objects yet. There's not even an extension for them. It's a bit of an oversight, but stems from the fact that they aren't in OpenGL ES 2.0 (which WebGL is based on) either.

Queries are useful for a number of things. Timer queries can be used to extract detailed profiling information about your rendering. Occlusion queries can be used for culling objects before they're drawn (especially useful if you have an expensive fragment shader). And so on.

This is a nuisance for me because I was using an occlusion query to perform fast pixel-accurate collision detection for my c++ game Schroedinger's Cat. Now that I'm attempting to port the game to WebGL, I need to find an alternative approach.

Update:
I've written a follow-up to this post: OpenGL ES and occlusion queries.

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