• Announcements

    • khawk

      Download the Game Design and Indie Game Marketing Freebook   07/19/17

      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.
Sign in to follow this  
Followers 0

[solved]Help with my ray picker

3 posts in this topic

Hey guys I'm trying to implement a simple ray picker in Opengl. In my little scene I have a green house that I would like to detect when the user clicks it. I am drawing the rays to the screen so I can debug them, so please have a look at these screenshots:
The red lines are the rays I have cast. The places I clicked are in the first screenshot on the outer endpoints of each ray. The problem is this projection to the far plane does not give accurate results if my goal is to determine if the user clicked the house or not. Should I be orthogonally projecting the rays from their origins? What can I do to fix this? Here is my code:
	Ray computePickingRay(int x, int y)
		glm::mat4 viewProj = projectionMatrix * camera->getViewMatrix();
		glm::mat4 invViewProj = glm::inverse(viewProj);
		int sx = gScreenWidth / 2;
		int sy = gScreenHeight / 2;
		glm::vec4 inV;
		inV.x = 1.0f * (x - sx) / (1.0f*sx);
		inV.y = 1.0f * ((gScreenHeight - y) - sy) / (1.0f * sy);
		inV.z = -1.0f;
		inV.w = 1.0f;
		glm::vec4 nearPlane = invViewProj * inV;
		inV.z = 1.0f;
		glm::vec4 farPlane = invViewProj * inV;
		glm::vec4 dir = (farPlane - nearPlane);
		Ray ray;
		ray.origin = vec3(nearPlane.x/nearPlane.w, nearPlane.y/nearPlane.w, nearPlane.z/nearPlane.w);
		ray.direction = glm::normalize(-vec3(dir.x/dir.w, dir.y/dir.w,dir.z/dir.w));
		return ray;




Share this post

Link to post
Share on other sites
Just a suggestion - If your only goal is to determine if the user clicked the house or not, there's a slightly easier way, that I think a lot of people use.
There's a (somewhat old) description here: http://www.lighthouse3d.com/opengl/picking/index.php3?color1 - I'm sure there's more tutorials out there
Edit: Another good explanation: http://content.gpwiki.org/index.php/OpenGL_Selection_Using_Unique_Color_IDs
1) Disable all shading - setting it to flat
2) Assign each object you want to pick a unique color. I did this once by basically making a list of the objects, and making each object's color be their list number, transformed to hex - so object at location 0 had color #000000, 1 had #000001, 2 - #000002... 10 - #00000A, etc.
3) Clear the backbuffer (or a FBO) with some color, I go with white because of the above
4) Draw the objects you want to pick
5) Read the pixel which the user clicked from the backbuffer
6) Translate the read in color back into a number ( hex->decimal conversion)
7) Clear the backbuffer again for future rendering

That's pretty much a pixel-perfect way to do picking. Edited by Milcho

Share this post

Link to post
Share on other sites
The origin of your rays appear to be wrong. For accurate picking, the origin of the ray should be the point on the near plane where the user clicked, and the direction of the ray should be the direction from the camera position to that point on the near plane.

Share this post

Link to post
Share on other sites

Thanks swiftcoder, that solved the problem! I changed the origin to the cameras position and direction to normalize(nearPlane - cameraPosition) and it works like a charm!


Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  
Followers 0