Texturing Only Part Of The Sphere

Texturing Only Part Of The Sphere

Scooter

Member #16,799

January 2018

Hi all:
I am trying to put 4 small textures, 90 degrees apart, on a sphere. I tried
to get pixels from the texture, convert to spherical coordinates and plot them
on the sphere. CodeBlocks was NOT happy and kicked it out with this error:
'free or corruption'. I thought this would have worked but didn't. I have
looked on the internet for a solution, but no go. I guess nobody has ever done
this sort of thing before. If someone could supply a small bit of code or a
direction on how to do this it would help me. I have posted some code above
to explain what I am trying to do. The textures are on the sphere but not
mapped to the sphere. Thanks for any help you can supply.
This was done on a linux machine.

Edgar Reynaldo

Major Reynaldo

May 2007

Scooter, it's called sphere mapping. It's been done before, you just have to know what you're talking about.

I ran your example code, and it works fine, the marios are plastered on the outside of the sphere in a quad. What did you expect? They won't map to the sphere unless you use a shader.

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jmasterx

Member #11,410

October 2009

Edgar Reynaldo said:

it's called sphere mapping. It's been done before,

Wait.... you mean to tell me people have made spheres with more than one texture

I thought Scooter was really on to something here with these multitextured spheres. Can't believe it's been done before

Agui GUI API -> https://github.com/jmasterx/Agui
Agui 0.2 Release Thread -> https://www.allegro.cc/forums/thread/612830

Edgar Reynaldo

Major Reynaldo

May 2007

jmasterx, play nice >:(

Scooter

Member #16,799

January 2018

Edgar:
SHADERS! I hate to hear that. There has got to be a simple way to map these
to the sphere. If not, I better stick to texturing flat objects. I am too new
to opengl to fool with shaders at this time. Thanks for the info.

Edgar Reynaldo

Major Reynaldo

May 2007

The inherent problem is that triangles are flat and coplanar and the surface of a sphere is not.

Scooter

Member #16,799

January 2018

Edgar:
Yeah I know! You just saved me from hours of frustration. Wished I had posted
this 2 weeks ago. From now on, I will stay away from curved surfaces.
Thanks again for helping me with the soccer ball. It looks neat!

Edgar Reynaldo

Major Reynaldo

May 2007

For a small example of what this problem entails, look up the Mercator Projection. It's the classic reverse of this problem, projecting a sphere onto a rectangle.

Since you have pentagons, you can paste your texture onto your pentagon, as long as you don't draw over the edge of the polygon, you're fine.

I should be able to adapt your soccer ball demo to use mario on a few of the pentagons in a little while.

{"name":"612336","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/f\/c\/fc347f54e755d602748eca7ce02c11c6.png","w":256,"h":256,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/f\/c\/fc347f54e755d602748eca7ce02c11c6"}

EDIT

Source file attached and image file as well.

{"name":"612339","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/5\/4\/549aa907c7e7dec2f71ab7d075b883f9.png","w":640,"h":360,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/5\/4\/549aa907c7e7dec2f71ab7d075b883f9"}

Scooter

Member #16,799

January 2018

Edgar:
Sorry I got tied up and couldn't get back to you. I downloaded your file but
I could not run it. Says it was a syntax error. It didn't tell me where it was.
I will try to track it down tomorrow. I could see by the photo that you were
indeed able to attach mario to a pentagon. Great job! I will get back to you
later.

Edgar Reynaldo

Major Reynaldo

May 2007

It's saved as C++. You could probably resave it as C and compile it with gcc. But it works just fine with g++. You have to link to allegro and opengl.