guanw@mcmaster.ca Phone

OpenGL – Part IV 

Weiguang Guan 

RHPCS, ABB 131-G 

Email: guanw@mcmaster.ca 

Phone: 905-525-9140 x 22540

Programming with OpenGL 

1. Introduction 

2. Drawing geometric objects 

3. Viewing 

4. Color 

5. Lighting 

6. Blending, antialiasing, and fog 

7. Display list 

8. Drawing pixels, bitmaps, fonts, and 

images 

9. Texture mapping 

10. Evaluators and NURBS 

11. Error handling

Drawing Pixels, Bitmaps, Fonts, and 

Images 

■ Image – (2D) rectangular array of data 

■ Bitmap – Binary image where each pixel is 

either 1 or 0. 

■ One usage of bitmap is creating fonts


Images 

■ Imaging pipeline (images, textures) 

■ Drawing bitmap


Images 

■ Pixel data storage 

glPixelStore*(GLenum 

glPixelStore*( GLenum pname, pname, 

TYPE param); param); 

pname (prefix: GL_PACK or GL_UNPACK): 

GL_UNPACK): 

ALIGNMENT – 1, 2, 4, 8 

ROW_LENGTH 

SKIP_ROWS 

SKIP_PIXELS 

SWAP_BYTES 

LSB_FIRST


Images 

■ Pixel data transfer operations 

void glPixelTransfer*(GLenum pname, pname, 

TYPE 

param); param); 

pname: pname 

GL_MAP_COLOR, GL_MAP_STENCIL, 

GL_INDEX_SHIFT, GL_INDEX_OFFSET, 

GL_INDEX_OFFSET 

GL_RED_ 

GL_GREEN_ 

GL_BLUE_SCALE, GL_BLUE_SCALE, 

BIAS 

GL_ALPHA_ 

GL_DEPTH_ 

GL_HUE GL_HUE_SCALE 

_SCALE x HUE + GL_HUE GL_HUE_BIAS 

_BIAS


Images 

■ Pixel data mapping 

void glPixelMap*(GLenum map, GLint 

mapsize, const TYPE *values); 

map: map: 

I_TO_I 

GL_PIXEL_MAP_ S_TO_S 

I_TO_R, G, B, A 

GL_PIXEL_MAP_H_TO_ 

GL_PIXEL_MAP_ _TO_H H (H : R, G, B, 

A)


Images 

■ Pixel data zooming 

void glPixelZoom(GLfloat zoomx, zoomx, 

GLfloat zoomy); zoomy); 

◆ Anisotropic zooming: zoomx ≠ zoomy 

◆ Mirroring: zoomx, zoomy < 0


Images 

■ Bitmaps and Fonts 

◆ glRasterPos*(…); 

✦ Raster position goes through Model/View 

and projection transformations the same 

way as vertices. 

✦ Bitmap is drawn at the current raster 

position. 

✦ Raster position is invalid if it is outside the 

viewing frustum. 

✦ Nothing is drawn if the current raster 

position is invalid, even though part of the 

bitmap to be drawn might be inside the 

viewing frustum.


Images 

yb 

o 

◆ glBitmap(GLsizei width, width, 

GLsizei height, height, 

GLfloat xbo, xbo, 

GLfloat ybo, ybo, 

GLfloat xbi, xbi, 

GLfloat ybi, ybi, 

const GLubyte* bitmap); bitmap); 

width 

xbo xbi 

ybi 

height


Images 

■ Code study 

◆ drawf.c 

✦ Fiddle with (xbo, ybo) and (xbi, ybi) 

✦ Change color of the bitmap font 

◆ font.c (using display list) 

■ Notice 

◆ Model/View transformations (scaling, rotation, 

translation) affect the current raster position 

only. They neither scale nor rotate bitmap. 

◆ GL_CURRENT_RASTER_COLOR is set to 

GL_CURRENT COLOR when glRasterPos(…) is 

called.


Images 

■ Reading Images 

◆ void glReadPixels(GLint x, , GLint y, , 

GLsizei width, width, 


GLenum 

format, format, 

GLenum type, type, 

GLvoid *pixels * pixels); ); 

(x,y x,y): ): lower-left corner; 

format: format: 

GL_RGB, GL_RED, GL_ALPHA, 

GL_LUMINANCE, 

GL_DEPTH_COMPONENT, etc. 

type: type: 

GL_UNSIGNED_BYTE, GL_INT, 

GL_FLOAT, etc.


Images 

◆ glReadBuffer(GLenum mode) mode) 

if doubledoublebuffering or stereo or both are enabled. 

mode: mode: 

GL_BACK, GL_FRONT, GL_LEFT, 

GL_RIGHT, GL_BACK_LEFT, GL_BACK_RIGHT, 

GL_FRONT_LEFT, GL_FRONT_RIGHT.


Images 

■ Drawing Images 

◆ void glDrawPixels(GLsizei width, width, 


GLenum format, format, 


const GLvoid *pixels * pixels); ); 

◆ void glDrawBuffer (GLenum mode); mode); 

■ Copying Images 

◆ void glCopyPixels(GLint x, , GLint y, , 



GLenum 

buffer); buffer);


Images 

■ Code Study 

◆ image.c




3. Viewing 

4. Color 

5. Lighting 




images 



11. Error handling

Texture Mapping 

■ What is texture? 

Image, texel 

■ Dimensionality: 1D, 2D, 3D 

■ What is texture mapping? 

Gluing texture on line (1D), object 

surface (2D), volume (3D) 

■ Hardware acceleration 

■ Only in RGBA mode


■ Mipmap – Level of detail


■ Type steps of using texture mapping 

◆ Create texture object and specify 

texture image 

◆ Specify how to modulate colors from 

texture and object 

◆ Enable texture mapping 

◆ Apply texture to object by specifying 

texture coordinates at vertices of 

object.


■ Specifying texture image 

void glTexImage2D(GLenum 

glTexImage2D(GLenum 

target, target, 

Glint level, level, 

GLint internalFormat, 

internalFormat, 



GLint 

border, border, 

GLenum format, format, 


const GLvoid *pixels * pixels); ); 

width, width, 

height must be power of 2. 

Example: 

glTexImage2D(GL_TEXTURE_2D, 0, 

GL_RGBA, 64, 64, 0, GL_RGBA, 

GL_UNSIGNED_BYTE, checkImage);


■ Color modulation 

glTexEnv*(GLenum target, target, 

GLenum 

pname, pname, 

TYPE param); param); 

target: target: 

must be GL_TEXTURE_ENV, 

pname: pname: 

must be 

GL_TEXTURE_ENV_MODE. 

Example: 

glTexEnvf(GL_TEXTURE_ENV, 

GL_TEXTURE_ENV_MODE, GL_DECAL);


■ Enable texture mapping 

glEnable(GL_TEXTURE_2D); 

■ Specifying texture coordinates 

glTexCoord*(…) 

Example: 

glTexCoord2f(0.0, 0.6); 

■ Other commands 

◆ glTexParameter*(…); 

◆ glTexSubImage2D(…); 

◆ glGenTexutres(…), glBindTexture(…), 

etc



◆ checker.c 

◆ texsub.c 

◆ mipmap.c




3. Viewing 

4. Color 

5. Lighting 




images 



11. Error handling

Evaluators and NURBS 

■ Evaluator 

◆ Curve – 1D 

✦ void glMap1{fd}(GLenum target, target, 

TYPE u1, u1, 

TYPE u2, u2, 

GLint stride, stride, 

GLint order, order, 

const 

TYPE* points); points); 

✦ glEvalCoord1*(…) 

✦ Example: 

glMap1f(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, 4, 

&ctrlpoints[0][0]); 

glEvalCoord1f(0.0); 

glEvalCoord1f(1.0);


◆ Surface – 2D 

✦ void glMap2{fd}(GLenum target, target, 

TYPE u1, u1, 

TYPE u2, u2, 

GLint ustride, ustride, 

GLint uorder, uorder, 

TYPE 

v1, v1, 

TYPE v2, v2, 

GLint vstride, vstride, 

GLint vorder, vorder, 

const TYPE* points); points); 

✦ glEvalCoord2*(…) 

✦ Example: 

glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 

1, 12, 4, &ctrlpoints[0][0][0]); 

glEvalCoord2f(0.0, 0.0); 

glEvalCoord2f(0.0, 1.0); 

glEvalCoord1f(1.0, 1.0);



◆ bezcurve.c 

◆ bezsurf.c 

◆ bezmesh.c


■ NURBS (GLU) 

◆ gluNewNurbsRenderer(); 

◆ gluNurbsProperty(…); 

◆ gluBeginSurface(…); 

✦ gluNurbsSurface(…); 

◆ gluEndSurface(…); 


◆ surface.c




3. Viewing 

4. Color 

5. Lighting 




images 



11. Error handling

Error Handling 

■ Commands that cause error are 

mostly ignored, and have NO effect 

on 

◆ OpenGL state 

◆ Framebuffer contents 

■ An error code is recorded by OpenGL 

once it detects an error caused by 

GL or GLU commands 

■ OpenGL error flag can record only 

one error code at a time.


■ Using glGetError() to query and 

reset error flag. It returns 

◆ GL_NO_ERROR, if no error detected so 

far, or 

◆ An error code, such as, 

GL_INVALID_VALUE, 

GL_STACK_OVERFLOW, etc 

■ Using gluErrorString(GLenum 

errorCode) errorCode) 

to interpret the error 

code, it returns a string describing 

the error.


■ Typical usage 

GLenum errCode; 

const GLubyte *errString; 

if ((errCode = glGetError()) ! 

=GL_NO_ERROR) 

{ 

} 

errString = gluErrorString(errCode); 

fprintf (stderr, "OpenGL Error: %s\n", 

errString);

Assignment 

■ Graphical “text editor” (referencing 

font.c) 

◆ Text that user types is dynamically 

displayed 

◆ Supprt “Backspace” key to erase 

characters

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