Picking

VitaliBR · 2012-08-26T14:17:50

Do you recommend I use this method? http://content.gpwiki.org/index.php/OpenGL:Tutorials:Picking I'm asking this, because I used it in my project and I have a problem. My cube in the scene has ID 1: The red square on top of the cube was made by me in photoshop. It is to show the area where I click and returns the selected cube. That is, the edges of the cube is shown by the function list_hits not selected anything, but I clicked on the edge of the cube!

Graphics and GPU Programming Programming OpenGL

Started by VitaliBR August 21, 2012 10:34 AM

14 comments, last by Rectangle 11 years, 7 months ago

larspensjo

1,561

August 23, 2012 04:17 PM

The Color picking would that be?

http://content.gpwik...nique_Color_IDs

Yes, the principles are right, but implemented using deprecated legacy OpenGL.

[size=2]Current project: Ephenation.
[size=2]Sharing OpenGL experiences: http://ephenationopengl.blogspot.com/

VitaliBR

147

Author

August 24, 2012 02:59 PM

[quote name='VitaliBR' timestamp='1345737964' post='4972620']
The Color picking would that be?

http://content.gpwik...nique_Color_IDs

Yes, the principles are right, but implemented using deprecated legacy OpenGL.
[/quote]

What is deprecated? glReadPixels?

http://mateusvitali.wordpress.com/

japro

887

August 24, 2012 03:04 PM

I was also wondering about this. For a game with a lot of selectable objects on screen and where you dont need to know wich triangle is under the cursor only wich object (lets say World of Warcraft) would it be best to use colour picking or ray tracing?

Usually you can get away with ray tracing against a simplified geometry (circles, ellipses, boxes...).

Tweet tweet!
My videos on YouTube
OpenGL Example Collection

larspensjo

1,561

August 24, 2012 06:44 PM

[quote name='larspensjo' timestamp='1345738643' post='4972630']
[quote name='VitaliBR' timestamp='1345737964' post='4972620']
The Color picking would that be?

http://content.gpwik...nique_Color_IDs

Yes, the principles are right, but implemented using deprecated legacy OpenGL.
[/quote]

What is deprecated? glReadPixels?
[/quote]
No, that is valid. The old ways are the use of glBegin(), glTranslatef(), glColor(), etc. It called "immediate mode", as you define the geometry on-the-fly. The correct way is to use Vertex Buffer Objects (VBO) and Vertex Array Objects (VAO). You will also have to define your own shader. At first glance, it looks much harder. And it is harder, to begin with.

For a general tutorial about OpenGL 3+, see Learning Modern 3D Graphics Programming or http://www.opengl-tutorial.org/.

[size=2]Current project: Ephenation.
[size=2]Sharing OpenGL experiences: http://ephenationopengl.blogspot.com/

V-man

813

August 26, 2012 01:14 PM

http://www.opengl.org/wiki/Common_Mistakes#Selection_and_Picking_and_Feedback_Mode

Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhLoadIdentityf2(matrix);
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhRotateAboutXf2(matrix, angleInRadians);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);