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      GameDev.net and CRC Press have teamed up to bring a free ebook of content curated from top titles published by CRC Press. The freebook, Practices of Game Design & Indie Game Marketing, includes chapters from The Art of Game Design: A Book of Lenses, A Practical Guide to Indie Game Marketing, and An Architectural Approach to Level Design. The GameDev.net FreeBook is relevant to game designers, developers, and those interested in learning more about the challenges in game development. We know game development can be a tough discipline and business, so we picked several chapters from CRC Press titles that we thought would be of interest to you, the GameDev.net audience, in your journey to design, develop, and market your next game. The free ebook is available through CRC Press by clicking here. The Curated Books The Art of Game Design: A Book of Lenses, Second Edition, by Jesse Schell Presents 100+ sets of questions, or different lenses, for viewing a game’s design, encompassing diverse fields such as psychology, architecture, music, film, software engineering, theme park design, mathematics, anthropology, and more. Written by one of the world's top game designers, this book describes the deepest and most fundamental principles of game design, demonstrating how tactics used in board, card, and athletic games also work in video games. It provides practical instruction on creating world-class games that will be played again and again. View it here. A Practical Guide to Indie Game Marketing, by Joel Dreskin Marketing is an essential but too frequently overlooked or minimized component of the release plan for indie games. A Practical Guide to Indie Game Marketing provides you with the tools needed to build visibility and sell your indie games. With special focus on those developers with small budgets and limited staff and resources, this book is packed with tangible recommendations and techniques that you can put to use immediately. As a seasoned professional of the indie game arena, author Joel Dreskin gives you insight into practical, real-world experiences of marketing numerous successful games and also provides stories of the failures. View it here. An Architectural Approach to Level Design This is one of the first books to integrate architectural and spatial design theory with the field of level design. The book presents architectural techniques and theories for level designers to use in their own work. It connects architecture and level design in different ways that address the practical elements of how designers construct space and the experiential elements of how and why humans interact with this space. Throughout the text, readers learn skills for spatial layout, evoking emotion through gamespaces, and creating better levels through architectural theory. View it here. Learn more and download the ebook by clicking here. Did you know? GameDev.net and CRC Press also recently teamed up to bring GDNet+ Members up to a 20% discount on all CRC Press books. Learn more about this and other benefits here.
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Super Llama

Poly/Ellipsoid Collision Response for Players and NPCs

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I've recently written a collision detection system for detecting collisions between ellipsoids (i.e. players, NPCs) and triangle lists. The detector works flawlessly using a ton of vector operations all baked into a few lines of scalar math, but I'm having trouble with the collision response. For a single triangle, this is easy, all I have to do is work out the closest point ON the triangle to the center of the sphere (I smash the coordinates into ellipsoid-scaled space so at this point it's just a sphere), and push it away from that point until the distance is greater than or equal to the radius.

Working with multiple triangles, I tried several approaches. First, I tried allowing any triangle the player collides with to push you away in turn, all on the same frame. This worked for 90 degree angles, but caused trouble with sharp angles and high-poly collisions since the player could end up on the edge of one of the small polys and be pushed directly into another one. Next, I tried finding the average of all "closest points" and using that as the hit position and moving away from there. While it worked far better than the previous method, the average point would sometimes be inside a sharp external corner, or not far enough out from a sharp internal corner. I have no idea how to calculate how far to push the ellipsoid from this hit position, and the only solution I can think of to stop the player from getting stuck is allowing movement away from the hit normal but not towards it, so they can leave simply by moving away from the point they're stuck in. The trouble with that is that you'll still phase slightly through a sharp spike or steep crevice. Though that might not be too big of a problem, it would make it easier to phase past a mesh and into the void if the penetration is deep enough.

One last problem arises with this method-- if the player is standing on the edge of a cliff or stair step, gravity will slowly pull him off due to the "push away from edge" concept. I suppose I could treat the bottom of the ellipsoid as flat, but I'd have to think of a new collision response for that too. Maybe I could use traces to check for footholds... I guess that's up to me how I want to handle it but any tips would be appreciated.

I wish I could just use binary space partitioning, but I don't want to have to write an editor/compiler for that and I'd prefer to just use 3dsmax to export single texture UV-mapped chunks of level geometry, which can then be arranged to make up a whole level. I guess I could also try forcing convex collision meshes though, but I'd still have the crevice problem between two convex bodies. Edited by Super Llama
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