[SOLVED] CS algorithm 15-462 Computer Graphics I Lecture 2

15-462 Computer Graphics I Lecture 2
Basic Graphics Programming
Basic Graphics Programming
Graphics Pipeline
Graphics Pipeline
OpenGL API
OpenGL API
Primitives: Lines, Polygons
Primitives: Lines, Polygons
Attributes: Color
Attributes: Color
Example
Example
[Angel Ch. 2]
[Angel Ch. 2]
January 16, 2003
Frank Pfenning
Carnegie Mellon University
http://www.cs.cmu.edu/~fp/courses/graphics/

A Graphics Pipeline
A Graphics Pipeline
Pipelines and parallelism
Latency vs throughput
Efficiently implementable in hardware
Notsoefficientlyimplementableinsoftware
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Programming a Pipeline
Programming a Pipeline
Specify the operation of each box Replace or accumulate
State and lack of modularity
Immediate mode graphics
On-line (OpenGL)
Modeling-rendering pipeline Off-line (Pixars Renderman)
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Vertices
Vertices
Vertices in world coordinates
voidglVertex3f(GLfloatx,GLfloaty,GLfloatz) Vertex (x, y, z) sent down the pipeline
Function call returns
Use GLtype for portability and consistency glVertex{234}{sfid}[v](TYPEcoords)
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Transformer
Transformer
Transformer in world coordinates
Mustbesetbeforeobjectisdrawn!
glRotatef(45.0, 0.0, 0.0, -1.0); glVertex2f(1.0, 0.0);
Complex [Angel Ch. 4]
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Clipper
Clipper
Mostlyautomaticfromviewport
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Projector
Projector
Complextransformation[AngelCh.5]
Orthographic
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Perspective
7

Rasterizer
Rasterizer
Interestingalgorithms[AngelCh.7] To window coordinates
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Outline
Outline
1. AGraphicsPipeline
2. TheOpenGLAPI
3. Primitives:vertices,lines,polygons 4. Attributes:color
5. Example:drawingashadedtriangle
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OpenGL Library Organization
OpenGL Library Organization
GLU (OpenGL Utility Library), modeling
GLUT(GLUtilityToolkit),windowsystem interface
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Graphics Functions
Graphics Functions
Primitive functions
Attributefunctions
Transformationfunctions Viewing functions
Inputfunctions
Control functions
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Outline
Outline
1. AGraphicsPipeline
2. TheOpenGLAPI
3. Primitives:vertices,lines,polygons 4. Attributes:color
5. Example:drawingashadedtriangle
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Primitives
Primitives
Specified via vertices General schema
glBegin(type); glVertex*(); glVertex*();
glEnd();
typedeterminesinterpretationofvertices
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Example: Square Outline
Example: Square Outline
Type GL_LINE_LOOP
glBegin(GL_LINE_LOOP); glVertex2f(0.0, 0.0); glVertex2f(1.0, 0.0); glVertex2f(1.0, 1.0); glVertex2f(0.0, 1.0);
glEnd();
zcoordinatedefaultsto0
Callstootherfunctionsareallowedbetween
glBegin(type) and glEnd();
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Points and Line Segments
Points and Line Segments
Makesenseinthreedimensions
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Polygons
Polygons
Polygons enclose an area
Rendering of area (fill) depends on attributes All vertices must be in one plane
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Polygon Restrictions
Polygon Restrictions
OpenGLPolygonsmustbesimple OpenGLPolygonsmustbeconvex
(a) simple, but not convex
convex
(b) non-simple
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Why Polygon Restrictions?
Why Polygon Restrictions?
Non-convex and non-simple polygons are expensive to process and render
Convexity and simplicity is expensive to test
BehaviorofOpenGLimplementationon
disallowed polygons is undefined
SometoolsinGLUfordecomposingcomplex
polygons (tessellation)
Trianglesaremostefficient
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Polygon Strips
Polygon Strips
Efficiencyinspaceandtime Reduces visual artefacts
Polygons have a front and a back, possibly with different attributes!
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Outline
Outline
1. AGraphicsPipeline
2. TheOpenGLAPI
3. Primitives:vertices,lines,polygons 4. Attributes:color
5. Example:drawingashadedtriangle
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Attributes
Attributes
Partofthestateofthegraphicspipeline Set before primitives are drawn
Remain in effect!
Examples:
Color, including transparency Reflection properties
Shading properties
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Physics of Color
Physics of Color
Electromagnetic radiation
Canseeonlytinypieceofthespectrum
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Color Filters
Color Filters
Eye can perceive only 3 basic colors
Computerscreensdesignedaccordingly
GR
Amplitude
B
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Color Spaces
Color Spaces
RGB(Red,Green,Blue)
Convenient for display
Can be unintuitive (3 floats in OpenGL)
HSV(Hue,Saturation,Value)
Hue: what color
Saturation: how far away from gray Value: how bright
Othersformoviesandprinting
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RGB vs HSV
RGB vs HSV
Apple Color Picker
BG
V
G
B
HS
25
R
R
R
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G
B
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Outline
Outline
1. AGraphicsPipeline
2. TheOpenGLAPI
3. Primitives:vertices,lines,polygons 4. Attributes:color
5. Example:drawingashadedtriangle
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Example: Drawing a shaded polygon
Example: Drawing a shaded polygon
Initialization:themainfunction
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); glutInitWindowSize (500, 500); glutInitWindowPosition (100, 100); glutCreateWindow (argv[0]);
init ();

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GLUT Callbacks
GLUT Callbacks
Window system independent interaction glutMainLoop processes events

glutDisplayFunc(display); glutReshapeFunc(reshape); glutKeyboardFunc (keyboard); glutMainLoop();
return 0;
} 01/16/2003
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Initializing Attributes
Initializing Attributes
Separate in init function
void init(void) {
glClearColor (0.0, 0.0, 0.0, 0.0);
/* glShadeModel (GL_FLAT); */
glShadeModel (GL_SMOOTH); }
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The Display Callback
The Display Callback
Handles exposure events
Install with glutDisplayFunc(display)
void display(void) {
glClear (GL_COLOR_BUFFER_BIT); /* clear buffer */
triangle (); glFlush ();
/* draw triangle */ /* force display */
}
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Drawing
Drawing
In world coordinates; remember state!
void triangle(void) {
glBegin (GL_TRIANGLES); glColor3f (1.0, 0.0, 0.0); /* red */ glVertex2f (5.0, 5.0);
glColor3f (0.0, 1.0, 0.0); /* green */ glVertex2f (25.0, 5.0);
glColor3f (0.0, 0.0, 1.0); /* blue */ glVertex2f (5.0, 25.0);
glEnd(); }
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The Image
The Image
Color of last vertex with flat shading glShadeModel(GL_FLAT) glShadeModel(GL_SMOOTH)
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Preview: Smooth Shading
Preview: Smooth Shading
Approximatingasphere
Flat Shading Smooth Shading
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Projection
Projection
Mappingworldtoscreencoordinates
void reshape(int w, int h) {
glViewport (0, 0, (GLsizei) w, (GLsizei) h); glMatrixMode (GL_PROJECTION); glLoadIdentity ();
if (w <= h)gluOrtho2D (0.0, 30.0, 0.0, 30.0 * (GLfloat) h/(GLfloat) w); elsegluOrtho2D (0.0, 30.0 * (GLfloat) w/(GLfloat) h, 0.0, 30.0); glMatrixMode(GL_MODELVIEW);}01/16/2003 15-462 Graphics I 34 ViewportViewport Determines clipping in window coordinates glViewPort(x,y,w,h)01/16/2003 15-462 Graphics I 35Orthographic ProjectionOrthographic Projection 2D and 3D versions glOrtho2D(left, right, bottom, top) In world coordinates!01/16/2003 15-462 Graphics I 36SummarySummary 1. AGraphicsPipeline2. TheOpenGLAPI3. Primitives:vertices,lines,polygons 4. Attributes:color5. Example:drawingashadedtriangle 01/16/2003 15-462 Graphics I 37 ReminderReminder ProgrammingAssignment1outtoday Due in two weeks Compilationinstructionsoncoursepage together with assignment Carefullyfollowaccountsetupinstructionsfor graphics lab (WeH 5336)01/16/2003 15-462 Graphics I 38