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OpenGL lighting

OpenGL

Started by PandaProtector23 Dec 11, 2011 at 11:50 PM 6 replies 2.5k views

Original Post

PandaProtector23

Dec 11, 2011 at 11:50 PM

Hi guys, it's my first post here

. A month ago i've start developing a game project with c++. I was aiming for 2D graphic and was using the Allegro Library. But, after some research on google, i found a game called Subvein, develop by Ben Johnson. And the graphic were very similar to what i needed for my game. So i've restart my project using OpenGL. Right now i'm working on the graphic engine. I want my game to be a top-down, tile base shooter. Right now, i can generated a map made of cube and apply texture to it. Now come the lighting effect. I've try to implement a basic lignting effect but i'm having some issue. The light just go through the cube i have draw and that make no sense to me. Since i'm new with 3D programming and OpenGL, i though maybe you guys can help me. I have join 1 screenshot showing the actual problem (don't mind the texture i was just too lazy to draw them now) and 1 paint image showing how i want the light to react. The red dot on both image show where the light source is. The light source is low enough so it's not lighting the top of the wall but mysteriously, it go across. If you need more info on what i'm using or what my code looks like, i will edit with all the information needed. thank you

ps. sorry for my bad english, i'm a french canadian.

V-man

Dec 12, 2011 at 12:05 AM

The light goes through other objects because GL is a forward renderer. You need to handle shadows on your own which is a complicated subject. You either need a raytracer or a radiosity renderer which probably require some offline renderer. Anything to generate shadow textures.

For real time, there is stencil shadow and shadow map techniques. For the shadow map technique, there are a lot of variations to the algorithm.

Just do some websearches.

PandaProtector23

Dec 12, 2011 at 1:49 AM

Okay thank you i'm looking into it right now. If i have some problem i will post again. Thank you

MarkS_

Dec 12, 2011 at 2:55 AM

Okay thank you i'm looking into it right now. If i have some problem i will post again. Thank you

Then please remove the "[SOLVED]" from the title. It is not and this is a question I have been waiting to ask, so I am equally interested in the answer.

PandaProtector23

Dec 12, 2011 at 4:06 PM

Hi again, i've look into shadow mapping and decide to go with it in my project. Do you know a basic OpenGL shadow mapping tutorial or example? I've try to understand the Paul's Project tutorial (http://www.paulsproj...ls/smt/smt.html) but i'm having difficulty to compile is code. He's using the extension [font="Arial"]ARB_depth_texture and ARB_shadow[/font][font="sans-serif"] [/font][font="Arial"]with GLee [/font][font="sans-serif"] [/font]and my IDE doesn't seem to appreciate it . Maybe someone have already hit the same problem as me or know another tutorial that is similar but not using GLee. Thank you

PandaProtector23

Dec 13, 2011 at 3:04 AM

Okay. I have implement a shadow map (well i've try) and the light is acting very weird. I have join a screenshot. What do you think this problem is associate to. Oh and now i don't have texture at all and it's normal because i've decide to try with a textureless version of my map first. Thank you.

second screenshot is when i use
GLfloat spot[] = {50.0f};
glLightfv(GL_LIGHT1, GL_SPOT_CUTOFF, spot);

PandaProtector23

Dec 13, 2011 at 6:22 PM

Hi. I'm posting this for those interested. I have understand what my mistake was in the last post (the weird looking shadow effect). I was using wrong projectionMatix and viewMatrix for my light, resulting in a non-sense shadow effect.

Right now, it look a lot better than it was, but i still have unusual shadow pattern and the shadow that are far still don't make sense. Someone told me that if i'm using shadow that are too far, i needed to cut my map in section and render shadow separately on every section. Someone know another technique?

I have implement a little red square that mark where the light is and key handler to move the light and camera around. I have taken other screenshot to show what i'm trying to explain.

PandaProtector23

Dec 14, 2011 at 3:50 AM

yes i'm posting again. Now i have improve a bit my shadow again but i really need someone to help me figure 2 or 3 thing. You can see a big part of my source code here: http://pastebin.com/sXTr2ets. I still have join some screenshot to show where I'm at with my work.

okay what i need help with is:

1- find a place and a way to squeeze my texture back in the code.
2- find a way to use multiple light (should i use 1 shadowMap for every light or 1 per light)
3- You can see it on the screenshot 5 and 6, pass a certain point, the shadow just continue align the way it was before he pass the point.

ps: i have delete all the screenshot from my other post to keep the post as clean as possible (it's not an album )

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