OpenGL Pixel Operations, Bitmaps, Fonts and Images The Current Raster Position Current raster position: A position in window coordinates where the next

OpenGL Pixel Operations, Bitmaps, Fonts and Images

The Current Raster Position

Current raster position: A position in window coordinates where the next bitmap (or image) is to be drawn.

void glRasterPos2{sifd}(TYPE x, TYPE y)void glRasterPos3{sifd}(TYPE x, TYPE y , TYPE z)

void glRasterPos {234}{sifd}v(TYPE * coords)

void glRasterPos4{sifd}(TYPE x, TYPE y , TYPE z , TYPE h)

Sets the current raster position. (x, y, z, h) is treated as object coordinates and is transformed by current modelview matrix, projection matrix and viewport. The transformed position is stored as current raster position.

Bitmap: An array of bit values (0 or 1).

Bitmaps

void glBitmap(GLsizei width, GLsizei height, GLfloat xo, GLfloat yo, GLfloat xi, GLfloat yi, const GLubyte * bitma

p)Draw a bitmap at current raster position.width, height: Width and height of the bitmap in pixels.xo, yo: Origin of the bitmap relative to its lower-left corner.xi, yi: x and y offsets to be added to the current raster position

after the bitmap is drawn.bitmap: Array that stores the bitmap

Pixel corresponding to “1” in bitmap is written using current raster color. Pixel corresponding to “0” in bitmap is unchanged.Current raster color is set to current color when glRasterPos*() is called.

The bits in a bitmap must be stored in chunks of 8 and start from lower left corner. But the width of the actually bitmap doesn't have to be multiple of 8.

0xff, 0xc0

GLubyte bitmap_F[] = {0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xff, 0x00, 0xff, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xc0, 0x00, 0xff, 0xc0, 0xff, 0xc0};glBitmap(10, 12, 0.0, 0.0, 11.0, 0.0, bitmap_F);

0xff, 0xc0

0xc0, 0x00

0xc0, 0x00

0xc0, 0x00

0xff, 0x00

0xff, 0x00

0xc0, 0x00

0xc0, 0x00

0xc0, 0x00

0xc0, 0x00

0xc0, 0x00

GLUT Bitmap Font

void glutBitmapCharacter(void *font, int character)

Render character with given font at current raster position. The width of the character is added to the x coordinate of current raster position. Internally GLUT implements this function using glBitmap().

font bitmap font

GLUT_BITMAP_8_BY_13 8 by 13 fixed width font

GLUT_BITMAP_9_BY_15 9 by 15 fixed width font

GLUT_BITMAP_TIMES_ROMAN_10 10-point Times Roman

GLUT_BITMAP_TIMES_ROMAN_24 24-point Times Roman

GLUT_BITMAP_HELVETICA_10 10-point Helvetica



To render a null-terminated string:

void DrawString(void *font, char *str){

while((*str)!='\0') {glutBitmapCharacter(font,(int)*str);str++;

}}

int glutBitmapWidth(void * font, int character)Return the width, in pixels, of character with given font

Using Fonts in Windows

BOOL wglUseFontBitmaps( HDC hdc, DWORD first, DWORD count, DWORD listBase)

hdc: Specifies the device context with the desired bitmap font. first: Specifies the first glyph. count: Specifies the number of glyphs.listBase: Specifies a starting display list.

This function creates count display lists in the current OpenGL rendering context. Each display list consists of a single call to glBitmap. Display list listBase+i corresponds to glyph first+i of the font currently selected in the device context specified by hdc, i = 0, 1, 2, ... , count 1.

HFONT hfont = CreateFont(......);SelectObject(hdc, hfont);

BOOL wglUseFontOutlines(HDC hdc, DWORD first, DWORD count, DWORD listBase, FLOAT deviation, FLOAT extrusion, int format, LPGLYPHMETRICSFLOAT lpgmf)

hdc: Specifies the device context with the desired outline font. first: Specifies the first glyph.count: Specifies the number of glyphs.listBase: Specifies a starting display list.deviation: Specifies the maximum chordal deviation from the original outlines.extrusion: Specifies how much a font is extruded in the negative z direction.format: WGL_FONT_LINES or WGL_FONT_POLYGONS.lpgmf : Points to an array of GLYPHMETRICSFLOAT structures that is to r

eceive the metrics of the glyphs. When lpgmf is NULL, no glyph metrics are returned.

This function creates count display lists in the current OpenGL rendering context. Display list listBase+i corresponds to glyph first+i of the font currently selected in the device context specified by hdc, i = 0, 1, 2, ... , count 1. The size of the font is 1.0 in x and y direction and extrusion in z direction.

Image Pipeline

Image: An array of pixel values. Pixel values are not limited to color values, they can also be depth values or stencil values.

OpenGL does not support reading images from or saving images to files.

SystemMemory

FrameBuffer

PixelStorageModes

Pixel TransferOperations(Pixel Map)

Unpack Pack

Rasterization(Pixel Zoom)

FragmentOperations

TextureMemory

Reading, Writing and Copying Pixel Data

Reading Pixel Data from Frame Buffer to System Memory

SystemMemory

FrameBuffer

PixelStorageModes


Unpack Pack


FragmentOperations

TextureMemory

void glReadPixels( GLint x, GLint y, GLsizei width, GLsizei height,GLenum format, GLenum type, GLvoid *pixels)

Read pixel data from a frame buffer rectangle to system memory.x, y: Lower left corner of the frame buffer rectanglewidth, height: Width and height of the frame buffer rectangleformat: Pixel data elements to be readtype: Data type of each pixel data elementpixels: System memory to receive pixel data

format Pixel data element

GL_RGB Red, Green, Blue components

GL_RGBA Red, Green, Blue, Alpha components

GL_BGR Blue, Green, Red components

GL_BGRA Blue, Green, Red, Alpha components

Pixel data element formats

format Pixel data element

GL_RED Red component

GL_GREEN Green component

GL_BLUE Blue component

GL_ALPHA Alpha component

GL_LUMINANCE Luminance component

GL_LUMINANCE_ALPHA Luminance and Alpha component

GL_STENCIL_INDEX Stencil value

GL_DEPTH_COMPONENT Depth value

Luminance = (Red + Green + Blue) / 3

Pixel data element formats (continued)

GL_BGR and GL_BGRA pixel formats were added in OpenGL 1.2.

type Data type

GL_UNSIGNED_BYTE unsigned 8-bit integer

GL_BYTE 8-bit integer

GL_UNSIGNED_SHORT unsigned 16-bit integer

GL_SHORT 16-bit integer

GL_UNSIGNED_INT unsigned 32-bit integer

GL_INT 32-bit integer

GL_FLOAT single-precision floating point

GL_BITMAP single bits in unsigned 8-bit integer

Normal data types for pixel data element

Each element is scaled to fit the range of the specified data type.

type Data type

GL_UNSIGNED_BYTE_3_3_2 packed unsigned 8-bit integer

GL_UNSIGNED_BYTE_2_3_3_REV packed unsigned 8-bit integer

GL_UNSIGNED_SHORT_5_6_5 packed unsigned 16-bit integer

GL_UNSIGNED_SHORT_5_6_5_REV packed unsigned 16-bit integer

GL_UNSIGNED_SHORT_4_4_4_4 packed unsigned 16-bit integer

GL_UNSIGNED_SHORT_4_4_4_4_REV packed unsigned 16-bit integer

GL_UNSIGNED_SHORT_5_5_5_1 packed unsigned 16-bit integer

GL_UNSIGNED_SHORT_1_5_5_5_REV packed unsigned 16-bit integer

GL_UNSIGNED_INT_8_8_8_8 packed unsigned 32-bit integer

GL_UNSIGNED_INT_8_8_8_8_REV packed unsigned 32-bit integer

GL_UNSIGNED_INT_10_10_10_2 packed unsigned 32-bit integer

GL_UNSIGNED_INT_2_10_10_10_REV packed unsigned 32-bit integer

Packed data types for pixel data element (added in OpenGL 1.2)

type Valid Pixel Element Formats

GL_UNSIGNED_BYTE_3_3_2 GL_RGB

GL_UNSIGNED_BYTE_2_3_3_REV GL_RGB

GL_UNSIGNED_SHORT_5_6_5 GL_RGB

GL_UNSIGNED_SHORT_5_6_5_REV GL_RGB

GL_UNSIGNED_SHORT_4_4_4_4 GL_RGBA, GL_BGRA

GL_UNSIGNED_SHORT_4_4_4_4_REV GL_RGBA, GL_BGRA

GL_UNSIGNED_SHORT_5_5_5_1 GL_RGBA, GL_BGRA

GL_UNSIGNED_SHORT_1_5_5_5_REV GL_RGBA, GL_BGRA

GL_UNSIGNED_INT_8_8_8_8 GL_RGBA, GL_BGRA

GL_UNSIGNED_INT_8_8_8_8_REV GL_RGBA, GL_BGRA

GL_UNSIGNED_INT_10_10_10_2 GL_RGBA, GL_BGRA

GL_UNSIGNED_INT_2_10_10_10_REV GL_RGBA, GL_BGRA

Valid pixel element formats for packed data types

Red Green Blue

01234567

GL_UNSIGNED_BYTE_3_3_2 with GL_RGB

RedGreenBlue

01234567

GL_UNSIGNED_BYTE_2_3_3_REV with GL_RGB

Example of packed data types:

RedGreenBlueAlpha

0123456789101112131415

GL_UNSIGNED_SHORT_4_4_4_4_REV with GL_RGBA

Red Green BlueAlpha

0123456789101112131415

GL_UNSIGNED_SHORT_4_4_4_4_REV with GL_BGRA

Red Green Blue Alpha

0123456789101112131415

GL_UNSIGNED_SHORT_4_4_4_4 with GL_RGBA

RedGreenBlue Alpha

0123456789101112131415

GL_UNSIGNED_SHORT_4_4_4_4 with GL_BGRA

Writing Pixel Data from System Memory to Frame Buffer

SystemMemory

FrameBuffer

PixelStorageModes


Unpack Pack


FragmentOperations

TextureMemory

void glDrawPixels( GLsizei width, GLsizei height,GLenum format, GLenum type, GLvoid *pixels)

Draw a rectangle of pixel data from system memory to frame buffer. The lower left corner of the pixel rectangle to be drawn is the current raster position.width, height: Width and height of the pixel rectangleformat: Pixel data elements to be writtentype: Data type of each pixel data elementpixels: System memory that stores the pixel dataformat and type have the same meaning as with glReadPixels().

Copying Pixel Data inside Frame Buffer

SystemMemory

FrameBuffer

PixelStorageModes


Unpack Pack


FragmentOperations

TextureMemory

void glCopyPixels( GLint x, GLint y, GLsizei width, GLsizei height,GLenum buffer)

Copy pixel data from one frame buffer rectangle (source) to another frame buffer rectangle (destination). The lower left corner of the destination rectangle is the current raster position.x, y: Lower left corner of the source rectanglewidth, height: Width and height of the pixel rectanglebuffer: GL_COLOR, GL_STENCIL, GL_DEPTH

Note: glCopyPixels() does not need data format or type information and it is not affected by pixel storage modes.

Pixel Storage Modes

Packing: The way in which pixel data is written to system memory.Unpacking: The way in which pixel data is read from system memory.

SystemMemory

FrameBuffer

PixelStorageModes


Unpack Pack


FragmentOperations

TextureMemory

void glPixelStorei(GLenum pname, GLint param)void glPixelStoref(GLenum pname, GLfloat param)

Set pixel storage modes. pname: parameter name. param: parameter value.

Parameter name Type Initial value Valid range

GL_UNPACK_ALIGNMENTGL_PACK_ALIGNMENT

GLint 4 1, 2, 4, 8

GL_UNPACK_SWAP_BYTESGL_PACK_SWAP_BYTES

GLboolean GL_FALSE GL_TRUE,GL_FALSE

GL_UNPACK_LSB_FIRSTGL_PACK_LSB_FIRST

GLboolean GL_FALSE GL_TRUE,GL_FALSE

GL_UNPACK_ROW_LENGTHGL_PACK_ROW_LENGTH

GLint 0 non-negative integer

GL_UNPACK_SKIP_ROWSGL_PACK_SKIP_ROWS


GL_UNPACK_SKIP_PIXELSGL_PACK_SKIP_PIXELS


LSB: Least Significant Bit.

*ALIGNMENT

Sets the byte alignment requirement for pixel data in system memory.1: Data is aligned on 8-bit address boundary in system memory2: Data is aligned on 16-bit address boundary in system memory4: Data is aligned on 32-bit address boundary in system memory8: Data is aligned on 64-bit address boundary in system memory

*SWAP_BYTES

Defines if the byte order in multi-byte data element is reversed.

*LSB_FIRST

Defines if the bits within a byte data are ordered from least significant bit to most significant bit.

*ROW_LENGTH, *SKIP_ROWS, *SKIP_PIXELS

These parameters are used when we only want to draw or read a sub-image of an entire image data in system memory.

Sub-Image

Image

*ROW_LENGTH

*SKIP_ROWS

*SKIP_PIXELS

Pixel Transfer Operations

Pixel transfer operations perform conversions on pixel data.

void glPixelTransferi(GLenum pname, GLint param)void glPixelTransferf(GLenum pname, GLfloat param)

void glPixelMapuiv(GLenum map, GLint size, const GLuint *values)void glPixelMapusv(GLenum map, GLint size, const GLushort *values)void glPixelMapfv(GLenum map, GLint size, const GLfloat *values)

Pixel Zoom

void glPixelZoom(GLfloat zx, GLfloat zy)

Set pixel zoom factors.zx: Pixel zoom factor in x direction. Default value is 1.0.zy: Pixel zoom factor in y direction. Default value is 1.0.

Zoom factors with magnitude greater than one magnify the image.Zoom factors with magnitude less than one minify the image.Negative zoom factors reflect the image about the current raster position.

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OpenGL Pixel Operations, Bitmaps, Fonts and Images The Current Raster Position Current raster position: A position in window coordinates where the next