• 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

Mouse X/Y ray to Sphere Intersection to world space point

1 post in this topic

Hi all,
I would like to do precise picking on a sphere surface, converting mouse X,Y to world space XYZ point so that I can draw object at that coord. Sounds simple enough and it should be, but I need some help ;)
I have built this simple test snippet that would simply create a some geo at the point on a globe where the mouse click ray intersection occurs and its nearly working! Its taking my xy casting that along the projection angle, taking into account the modelView inv (camera pos) etc.  The only thing that I have an issue is that intersection with the Y coordinate is upside-down, also strangely  I have to swap the Z coord of the mouse ( so ray_start = [x,y,1] and ray_dest = [x,y,0] otherwise its rejected as pointing backwards .  
So, that done, clicking around the equator of the sphere it plots the geo's nicely at the x and y moving orbit the camera left/right it works fine, but plotting above of the center screen creates geo points south or downward and clicking below center screen viceversa plots mirrored north .  Simply swapping the final vector does not work as its the intersection thats matters.  I know I am so close.. I looking at the computeWindow Matrix calculation as a potential culprit. I Just need a little more light I really appreciate some help if possible.  
Many thanks for any help!  
(This test code is in webGL and javascript)
// window matrix function (where I think the problem could be)
this.computeWindowMatrix = function(xstart, ystart, width, height) {
   var translate = osg.Matrix.makeTranslate(1.0, 1.0, 1.0);
   var scale = osg.Matrix.makeScale(0.5*width, 0.5*height, 0.5);
   var offset = osg.Matrix.makeTranslate(xstart,ystart,0.0);
   return osg.Matrix.preMult(offset, osg.Matrix.preMult(scale, translate));
    var ray_start = [x,y,1];  //had to swap the Z so its cast forward
    var ray_dest  = [x,y,0];
    var matrix = osg.Matrix.makeIdentity();
    var w = osg.Matrix.copy(viewer.view.viewport.computeWindowMatrix(), []);
    var p = viewer.view.getProjectionMatrix();
    var m = viewer.view.getViewMatrix();
    osg.Matrix.preMult(matrix, w);
    osg.Matrix.preMult(matrix, p);
    osg.Matrix.preMult(matrix, m);
    var inv = [];
    var valid = osg.Matrix.inverse(matrix, inv);
    var ns = osg.Matrix.transformVec3(inv, ray_start, new Array(3));
    var ne = osg.Matrix.transformVec3(inv, ray_dest, new Array(3));
   //======Ray-Sphere intersection========
    var t0, t1; // parametric solutions for t if the ray intersects
    var radius2 = (6371* 6371);
    var ray_dir = osg.Vec3.normalize(osg.Vec3.sub(ns,ne, []) ,[]);
    var L = osg.Vec3.sub([0,0,0],ns,[]);
    var tca = osg.Vec3.dot(L,ray_dir);
    if (tca < 0) return false;   //wrong direction
    var d2 = osg.Vec3.dot(L,L) - (tca * tca);  //o2=h2-a2
    if (d2 > radius2) return false; //overshoots
    var thc = Math.sqrt(radius2 - d2);  //find the exit point
    t0 = tca - thc;
    t1 = tca + thc;
    //Draw a box at the world point    
    var hitPoint = osg.Vec3.add(ns, osg.Vec3.mult(ray_dir,t0,[]),[]);
    var geometry = osg.createTexturedBox(0, 0, 0, 1000,1000,1000);
    var xform     = new osg.MatrixTransform()

Share this post

Link to post
Share on other sites
Fixed it ;) For any interested please read.
Yes as I thought it was the t[font=verdana, arial, 'Bitstream Vera Sans', helvetica, sans-serif]he viewport transformation to NDC (normalized device coordinate ) coordinates:[/font]
Code changed to this fixed it.

ray_start[0] = (x / viewer.view.viewport.width()) * 2 - 1;

ray_start[1] = -(y / viewer.view.viewport.height()) * 2 + 1;

ray_start[2] = 1;

ray_dest[0] = (x / viewer.view.viewport.width()) * 2 - 1;

ray_dest[1] = -(y / viewer.view.viewport.height()) * 2 + 1;

ray_dest[2] = 0;

Wilson Edited by handsfelloff

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