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Color and Lighting

Color and Lighting. Color 1/5. Two Color modes: RGBA Color Index Choosing between RGBA and Color Index glutInitDisplayMode(); (GLUT) glutInitDisplayMode(GL_RGBA) for RGBA glutInitDisplayMode(GL_INDEX) for color index. Color 2/5. RGBA mode:

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Color and Lighting

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  1. Color and Lighting Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  2. Color1/5 • Two Color modes: • RGBA • Color Index • Choosing between RGBA and Color Index • glutInitDisplayMode(); (GLUT) • glutInitDisplayMode(GL_RGBA) for RGBA • glutInitDisplayMode(GL_INDEX) for color index Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  3. Color2/5 • RGBA mode: • Four components Red, Green, Blue, and Alpha. • Each component is normalize to 0.0~1.0 • glColor{34}{sifd}[v](TYPE colors); • Ex. • glColor3f(0.0, 0.0, 0.0); black color • glColor4f(0.0, 1.0, 0.0, 1.0); green color Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  4. Color3/5 • Color Index mode: • Use a color map (lookup table) to prepare for a paint-by-number scene. • OpenGL does not provide any routing to load color map (it’s load by window system). • glIndex{sidf…}(TYPE c); Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  5. Color4/5 • Clearing the color buffer • Use glClearColor() or glClearIndex() to specify the clear color. • Call glClear(GL_COLOR_BUFFER_BIT); if need to clear the color buffer. • Specifying shading model • glShadeModel(GLenum mode); • The parameter is either GL_FLAT or GL_SMOOTH (default). Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  6. GL_FLAT GL_SMOOTH Color5/5 Consider the following code with different shading model: glBegin(GL_POLYGON); glColor3f(1.0, 1.0, 1.0); glVertex2f(-0.5, 0.-0.5); glColor3f(0.0, 0.0, 1.0); glVertex2f(0.5, 0.-0.5); glColor3f(1.0, 1.0, 0.0); glVertex2f(0.0, 0.5); glEnd(); Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  7. Hidden-Surface Removal • How to apply HSR in OpenGL: • glutInitDisplayMode(GLUT_DEPTH); • Enable the depth buffer. • glEnable(GL_DEPTH_TEST); • Enable depth test. • In display function • glClear(GL_DEPTH_BUFFER_BIT); when you wish to clean the depth buffer. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  8. Lights in OpenGL1/2 • Ambient light • Light that has been scattered by the environment. • Diffuse light • Light that come from one direction. • Specular light • Light that come from particular direction that tend to bounce off the surface in a preferred direction. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  9. Lights in OpenGL2/2 Three different kinds of lights on a white ball. Specular light : white Diffuse light : yellow Ambient light : red Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  10. Material in OpenGL1/3 • Material • Describe the percentages of the incoming red, green, blue light it reflects on a surface. • Diffuse • The most important role in determining what you perceive the color of an object to be. • Affected by the color of the incident diffuse light and the angle of the incident light relative to the normal direction • Ambient • Affected by the global ambient light and ambient light from individual light sources. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  11. Material in OpenGL2/3 • Specular & Shininess • Specular reflection from an object produces highlights. • The amount of specular reflection seen by a viewer does depend on the location of the viewpoint. • Shininess control the size and brightness of the highlight. • Emission • Make an object appear to be giving off light of that color. • Since most real-world objects (except lights) don't emit light, you'll probably use this feature mostly to simulate lamps and other light sources in a scene. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  12. Material in OpenGL3/3 A white light on the ball that has following materials: Specular : blue Diffuse : red Ambient : green Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  13. Put light into OpenGL • How to apply lighting in OpenGL • Use glEnable( GL_LIGHTING ) to enable lighting. • Enable and set properties for light sources. • Up to 8 lights are available (GL_LIGHT0 ~ GL_LIGHT7). • Enable a light by calling to glEnable( GL_LIGHTi ) . • Set light properties by calling to glLightfv( … ) . • Set light model by calling to glLightModelfv( … ). • Define material properties for objects in the scene by calling to glMaterialfv( … ) . • Assign normal vectors for each vertex of every object. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  14. Lighting Sample1/4 #include <GL/glut.h> void init() { GLfloat mat_diffuse[] = {1.0, 0.0, 0.0, 1.0}; GLfloat mat_specular[] = {0.0, 0.0, 1.0, 1.0}; GLfloat mat_ambient[] = {0.0, 1.0, 0.0, 1.0}; GLfloat mat_shininess[] = {50.0}; GLfloat light_specular[] = {1.0, 1.0, 1.0, 1.0}; GLfloat light_diffuse[] = {1.0, 1.0, 1.0, 1.0}; GLfloat light_ambient[] = {0.0, 0.0, 0.0, 1.0}; GLfloat light_position[] = {5.0, 5.0, 10.0, 0.0}; glClearColor(0.0, 0.0, 0.0, 0.0); glShadeModel(GL_SMOOTH); // z buffer enable glEnable(GL_DEPTH_TEST); // enable lighting glEnable(GL_LIGHTING); Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  15. Lighting Sample2/4 // set light property glEnable(GL_LIGHT0); glLightfv(GL_LIGHT0, GL_POSITION, light_position); glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse); glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular); glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient); // set material property glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse); glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular); glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient); glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess); } void GL_display() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glutSolidSphere(0.8, 128, 128); glFlush(); } Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  16. Lighting Sample3/4 void reshape (int w, int h) { glViewport (0, 0, (GLsizei) w, (GLsizei) h); glMatrixMode (GL_PROJECTION); glLoadIdentity(); glOrtho (-1.0, 1.0, -1.0, 1.0, -1.0, 1.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } int main(int argc, char** argv) { glutInit(&argc, argv); glutInitWindowSize(400, 400); glutInitWindowPosition(0, 0); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA | GLUT_DEPTH); glutCreateWindow("Planet"); init(); glutDisplayFunc(GL_display); glutReshapeFunc(reshape); glutMainLoop(); } Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  17. Lighting Sample4/4 Lighting enabled Lighting disabled Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  18. Lighting: Normal Vector1/2 • Assign normal vectors for each vertex of every object • glNormal{34}{isfd}[v](TYPE* normal); • Assign normal vector for vertices (the normal vector should be assigned before you assign vertex). • Normal vectors must be normalize. OpenGL can automatically normalize normal vector by glEnable( GL_NORMALIZE ) . • In the previous sample, the normal for the sphere are defined as part of the glutSolidSphere() routine. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  19. Lighting: Normal Vector2/2 • Example void GL_Display() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glBegin(GL_POLYGON); glNormal3f(0.0, 1.0, 0.0); glVertex3f(1.0, 0.0, 0.0); glVertex3f(0.0, 0.0, -1.0); glVertex3f(-1.0, 0.0, 0.0); glEnd(); glFlush(); } Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  20. Lighting: Light Source1/7 • Enable and set properties for light sources • Use glEnable(GL_LIGHT0); to enable light zero. You can use at most 8 light sources in OpenGL spec. (GL_LIGHT0~GL_LIGHT7) • GL_LIGHTi can be rewritten as GL_LIGHT0 + i. • glLight{if}[v](GLenum light, Glenum pname, TYPE param); • Specify the attribute of light • light can be GL_LIGHT0 ~ GL_LIGHT7 • pname is the characteristic of the light • param is the value of pname. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  21. Pname Def. Value Meaning GL_AMBIENT (0.0, 0.0, 0.0, 0.0) ambient RGBA intensity of light GL_DIFFUSE (1.0, 1.0, 1.0, 1.0) diffuse RGBA intensity of light GL_SPECULAR (1.0, 1.0, 1.0, 1.0) specular RGBA intensity of light GL_POSITION (0.0, 0.0, 1.0, 0.0) (x, y, z, w) position of light GL_SPOT_DIRECTION (0.0, 0.0, -1.0) (x, y, z) direction of spotlight GL_SPOT_EXPONENT 0.0 spotlight exponent GL_SPOT_CUTOFF 180.0 spotlight cutoff angle GL_CONSTANT_ATTENUATION 1.0 constant attenuation factor GL_LINEAR_ATTENUATION 0.0 linear attenuation factor GL_QUADRATIC_ATTENUATION 0.0 quadratic attenuation factor Lighting: Light Source2/7 Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  22. Lighting: Light Source3/7 • Color • The default values listed for GL_DIFFUSE and GL_SPECULAR apply only to GL_LIGHT0. • For other lights, the default value is (0.0, 0.0, 0.0, 1.0 ) for GL_DIFFUSE, GL_SPECULAR and GL_AMBIENT. • Position ( x, y, z, w ) • W is ZERO, Directional light, (x,y,z) specify its direction. • W is NONZERO, Positional light, (x,y,z) specify the location of the light source. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  23. Lighting: Light Source4/7 • Attenuation • d = distance between the light's position and the vertex • kc = GL_CONSTANT_ATTENUATION • kl = GL_LINEAR_ATTENUATION • kq = GL_QUADRATIC_ATTENUATION • If light is directional light, the attenuation is always 1 Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  24. Lighting: Light Source5/7 • How to create spot light • Define your light as positional light • Define light spot direction GLfloat spot_direction[] = { -1.0, -1.0, 0.0 }; glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, spot_direction); • Define light spot exponent glLightf(GL_LIGHT1, GL_SPOT_EXPONENT, 2.0); • Define light spot cutoff • The value for GL_SPOT_CUTOFF is restricted to being within the range [0.0,90.0] (unless it has the special value 180.0 (default)). Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  25. Lighting: Light Source6/7 Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  26. Lighting: Light Source7/7 • Control a Light’s Position and Direction • OpenGL treats the position and direction of a light source just as it treats the position of a geometric primitive. • The MODELVIEW transformation will also be applied to light sources. • Any matrix operations can also apply to light sources. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  27. Lighting: Lighting Model1/2 • Selecting a lighting model • void glLightModel{if}[v](GLenum pname, TYPE[*] param); • Sets properties of the lighting model. • The lighting model is used to control the global behaviors of all the lights. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  28. Pname Def. Value Meaning GL_LIGHT_MODEL_AMBIENT (0.2, 0.2, 0.2, 1.0) ambient RGBA intensity of the entire scene GL_LIGHT_MODEL_LOCAL_VIEWER 0.0 or GL_FALSE how specular reflection angles are computed GL_LIGHT_MODEL_TWO_SIDE 0.0 or GL_FALSE choose between one-sided or two- sided lighting Lighting: Lighting Model2/2 Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  29. Lighting: Material1/6 • Define material properties for objects in the scene. • void glMaterial{if}[v](GLenum face, GLenum pname, TYPE[*] param); • Specifies a current material property for use in lighting calculations. • face can be GL_FRONT, GL_BACK, or GL_FRONT_AND_BACK. • The particular material property being set is identified by pname and the desired values for that property are given by param. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  30. Pname Def. Value Meaning GL_AMBIENT (0.2, 0.2, 0.2, 1.0) ambient color of material GL_DIFFUSE (0.8, 0.8, 0.8, 1.0) diffuse color of material GL_AMBIENT_AND_DIFFUSE ambient and diffuse color of material GL_SPECULAR (0.0, 0.0, 0.0, 1.0) specular color of material GL_SHININESS 0.0 specular exponent GL_EMISSION (0.0, 0.0, 0.0, 1.0) emissive color of material GL_COLOR_INDEXES (0, 1, 1) ambient, diffuse, and specular color indices Lighting: Material2/6 Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  31. No Ambient Gray Ambient Blue Ambient Diffuse Only Specular Higher Shininess Emission Lighting: Material3/6 Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  32. Lighting: Material4/6 • Performance issue • glMaterialfv(); is called repeatedly to set different material properties for different objects. • glMaterial*() has a performance cost associate with its use. • Another technique for minimizing performance costs associated with changing material properties is to use glColorMaterial(); Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  33. Lighting: Material5/6 • glColorMaterial(GLenum face, GLenum mode); • Causes the material property of the specified material face to track the value of the current color at all times. • face parameter can be GL_FRONT, GL_BACK, or GL_FRONT_AND_BACK (default). • mode parameter can be GL_AMBIENT, GL_DIFFUSE, GL_AMBIENT_AND_DIFFUSE (the default), GL_SPECULAR, or GL_EMISSION. • A change to the current color (using glColor*()) immediately updates the specified material properties. • Use glEnable(GL_COLOR_MATERIAL); to enable color material. • glColorMaterial() has no effect on color-index lighting. Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  34. Lighting: Material6/6 • Following is a example that using color material to change the ambient and diffuse glEnable(GL_COLOR_MATERIAL); glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE); glBegin(GL_POLYGON); glNormal3f(0.0, 1.0, 0.0); glColor3f(1.0, 0.0, 0.0); glVertex3f(-0.5, -0.5, -0.5); glColor3f(0.0, 0.0, 1.0); glVertex3f(0.5, -0.5, -0.5); glColor3f(0.0, 1.0, 0.0); glVertex3f(0.0, 0.5, 0.5); glEnd(); Tan-Chi Ho, CGGM Lab., CSIE of NCTU

  35. Any Question? ? Tan-Chi Ho, CGGM Lab., CSIE of NCTU

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