OpenGL L04-Lighting
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This document discusses lighting techniques in OpenGL, including: - Setting up light sources by defining light properties like ambient, diffuse, specular intensities and position. - Defining material properties like ambient, diffuse, specular colors and shininess for objects. - The importance of normals for calculating how light interacts with surfaces. - Examples of implementing directional, spot and other types of lights. - Techniques for generating shadows by re-drawing objects projected onto a shadow plane.
![Colors in OpenGL
• glColor3f(red, green, blue) [0,1]
• glColor4f(red, green, blue, alpha) [0,1]](https://image.slidesharecdn.com/opengll04-lighting-140906092215-phpapp02/85/OpenGL-L04-Lighting-8-320.jpg)
![Colors in OpenGL
• glColor3f(red, green, blue) [0,1]
• glColor4f(red, green, blue, alpha) [0,1]
– alpha for transparency [0; full,1: no]](https://image.slidesharecdn.com/opengll04-lighting-140906092215-phpapp02/85/OpenGL-L04-Lighting-9-320.jpg)
![Lighting in OpenGL – Light Source
• For the light source:
– Set light properties:
float Light_Ambient [ ] = {0.2,0.2,0.2,1};
float Light_Diffuse [ ] = {1,1,1,1};
float Light_Specular [ ] = {1,1,1,1};
float Light_Position [ ] = {0,0,20,0};
– Enable a specific light (GL_LIGHT0):
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
– Bind the light properties with the specific light (GL_LIGHT0):
glLightfv(GL_LIGHT0 , GL_AMBIENT , Light_Ambient);
glLightfv(GL_LIGHT0 , GL_DIFFUSE , Light_Diffuse);
glLightfv(GL_LIGHT0 , GL_SPECULAR , Light_Specular);
glLightfv(GL_LIGHT0 , GL_POSITION , Light_Position);](https://image.slidesharecdn.com/opengll04-lighting-140906092215-phpapp02/85/OpenGL-L04-Lighting-25-320.jpg)
![Lighting in OpenGL – Object Material
• For the object material:
– Set material properties:
float Cone_Ambient [ ] = {0.1,0.1,0.1,1};
float Cone_Diffuse [ ] = {0.2,0.1,0.9,1};
float Cone_Specular [ ] = {1,1,1,1};
float Cone_Shininess = 100;
– Bind the material properties with a specific object:
glMaterialfv(GL_FRONT_AND_BACK , GL_AMBIENT , Cone_Ambient);
glMaterialfv(GL_FRONT_AND_BACK , GL_DIFFUSE , Cone_Diffuse);
glMaterialfv(GL_FRONT_AND_BACK , GL_SPECULAR , Cone_Specular);
glMaterialf (GL_FRONT_AND_BACK , GL_SHININESS , Cone_Shininess);
• Now draw whatever you want.
GLUquadric *quadric = gluNewQudric();
gluCylinder(quadric, 4, 1, 7, 32, 32);](https://image.slidesharecdn.com/opengll04-lighting-140906092215-phpapp02/85/OpenGL-L04-Lighting-26-320.jpg)
OpenGL L04-Lighting
- 2. What we’ve learnt so far..
- 4. Lighting
- 5. How We See Things?
- 6. How We See Things?
- 7. Light and Color Systems Additive Colors Subtractive Colors
- 8. Colors in OpenGL • glColor3f(red, green, blue) [0,1] • glColor4f(red, green, blue, alpha) [0,1]
- 9. Colors in OpenGL • glColor3f(red, green, blue) [0,1] • glColor4f(red, green, blue, alpha) [0,1] – alpha for transparency [0; full,1: no]
- 10. Color Filling Mode • Filling Mode – glShadeModel(GL_FLAT); • Fill the polygon with solid color (the same as last vertex color) – glShadeModel(GL_SMOOTH); • Interpolate colors between polygon edges
- 11. Light’s Type • DIFFUSE color's alpha value actually determines the transparency of the polygon Only ambient light only specular lightonly diffuse light
- 12. The Modified Phong Model • Computes a color or shade for each vertex using a lighting model (the modified Phong model) that takes into account – Diffuse reflections – Specular reflections – Ambient light – Emission • Vertex shades are interpolated across polygons by the rasterizer
- 13. Lighting - Types • Ambient Light: doesn’t come from any particular direction. It has an original source somewhere, but the rays of light have bounced around the room or scene and become directionless.
- 14. Lighting - Types • Diffuse Light: The diffuse part of an OpenGL light is the directional component that appears to come from a particular direction and is reflected off a surface with an intensity proportional to the angle at which the light rays strike the surface. Thus, the object surface is brighter if the light is pointed directly at the surface than if the light grazes the surface from a greater angle.
- 15. Lighting - Types • Specular light: Like diffuse light, specular light is a highly directional property, but it interacts more sharply with the surface and in a particular direction.
- 16. The Modified Phong Model • The model is a balance between simple computation and physical realism • The model uses – Light positions and intensities – Surface orientation (normals) – Material properties (reflectivity) – Viewer location • Computed for each source and each color component
- 17. Material Properties • Define the surface properties of a primitive • you can have separate materials for front and back Property Description Diffuse Base object color Specular Highlight color Ambient Low-light color Emission Glow color Shininess Surface smoothness
- 18. Material Properties • Define the surface properties of a primitive • you can have separate materials for front and back Property Description GL_DIFFUSE Base color GL_SPECULAR Highlight Color GL_AMBIENT Low-light Color GL_EMISSION Glow Color GL_SHININESS Surface Smoothness
- 19. Color Theory
- 20. Color Theory
- 22. Lighting in OpenGL Light Source and Object Material
- 23. Lighting in OpenGL Light Source and Object Material
- 24. Turning on the Lights • For any type of light, you should first – Flip each light’s switch glEnable(GL_LIGHT0); – Turn on the power glEnable(GL_LIGHTING);
- 25. Lighting in OpenGL – Light Source • For the light source: – Set light properties: float Light_Ambient [ ] = {0.2,0.2,0.2,1}; float Light_Diffuse [ ] = {1,1,1,1}; float Light_Specular [ ] = {1,1,1,1}; float Light_Position [ ] = {0,0,20,0}; – Enable a specific light (GL_LIGHT0): glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); – Bind the light properties with the specific light (GL_LIGHT0): glLightfv(GL_LIGHT0 , GL_AMBIENT , Light_Ambient); glLightfv(GL_LIGHT0 , GL_DIFFUSE , Light_Diffuse); glLightfv(GL_LIGHT0 , GL_SPECULAR , Light_Specular); glLightfv(GL_LIGHT0 , GL_POSITION , Light_Position);
- 26. Lighting in OpenGL – Object Material • For the object material: – Set material properties: float Cone_Ambient [ ] = {0.1,0.1,0.1,1}; float Cone_Diffuse [ ] = {0.2,0.1,0.9,1}; float Cone_Specular [ ] = {1,1,1,1}; float Cone_Shininess = 100; – Bind the material properties with a specific object: glMaterialfv(GL_FRONT_AND_BACK , GL_AMBIENT , Cone_Ambient); glMaterialfv(GL_FRONT_AND_BACK , GL_DIFFUSE , Cone_Diffuse); glMaterialfv(GL_FRONT_AND_BACK , GL_SPECULAR , Cone_Specular); glMaterialf (GL_FRONT_AND_BACK , GL_SHININESS , Cone_Shininess); • Now draw whatever you want. GLUquadric *quadric = gluNewQudric(); gluCylinder(quadric, 4, 1, 7, 32, 32);
- 28. Lighting Example
- 29. SpotLight Lighting Example Complete Code
- 30. Lighting Example
- 32. Why Normals are essential for lighting?
- 33. Why Normals are essential for lighting?
- 34. Normals for Lighting • Vertex Normals – Prefixed w/ “vn” (Wavefront) – Contains x,y,z of normal – Not necessarily unit length – Not necessarily in vertex order – Indexed as with vertices (x0,y0,z0) (a0,b0,c0) (u0,v0) (x1,y1,z1) (a1,b1,c1) (u1,v1) (x2,y2,z2) (a2,b2,c2) (u2,v2)
- 35. Surface Normals • Normals define how a surface reflects light – Application usually provides normals as a vertex atttribute – Current normal is used to compute vertex’s color – Use unit normals for proper lighting • scaling affects a normal’s length
- 39. Shadowing
- 40. Shadowing • How to make a shadow? – Draw the whole object again, projecting it on the shadow plane (the plane in which the shadow will appear)
- 41. Shadowing