Open GL Pixel Operations Bitmaps Fonts and Images

Open. GL 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 gl. Raster. Pos 2{sifd}(TYPE x, TYPE y) void gl. Raster. Pos 3{sifd}(TYPE x, TYPE y , TYPE z) void gl. Raster. Pos 4{sifd}(TYPE x, TYPE y , TYPE z , TYPE h) void gl. Raster. Pos {234}{sifd}v(TYPE * coords) 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.

Bitmaps Bitmap: An array of bit values (0 or 1). void gl. Bitmap(GLsizei width, GLsizei height, GLfloat xo, GLfloat yo, GLfloat xi, GLfloat yi, const GLubyte * bitmap) 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 gl. Raster. Pos*() 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. 0 xff, 0 xc 0, 0 xc 0, 0 xff, 0 xc 0, 0 xc 0, 0 x 00 0 x 00 0 x 00 GLubyte bitmap_F[] = {0 xc 0, 0 x 00, 0 xc 0, 0 x 00, 0 xff, 0 x 00, 0 xc 0, 0 x 00, 0 xff, 0 xc 0}; gl. Bitmap(10, 12, 0. 0, 11. 0, 0. 0, bitmap_F);

GLUT Bitmap Font void glut. Bitmap. Character(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 gl. Bitmap(). 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_1 0 10 -point Times Roman GLUT_BITMAP_TIMES_ROMAN_2 4 24 -point Times Roman GLUT_BITMAP_HELVETICA_10 10 -point Helvetica GLUT_BITMAP_HELVETICA_12 12 -point Helvetica GLUT_BITMAP_HELVETICA_18 18 -point Helvetica

int glut. Bitmap. Width(void * font, int character) Return the width, in pixels, of character with given font To render a null-terminated string: void Draw. String(void *font, char *str) { while((*str)!='') { glut. Bitmap. Character(font, (int)*str); str++; } }

Using Fonts in Windows HFONT hfont = Create. Font(. . . ); Select. Object(hdc, hfont); BOOL wgl. Use. Font. Bitmaps( HDC hdc, DWORD first, DWORD count, DWORD list. Base) hdc: first: count: list. Base: Specifies the device context with the desired bitmap font. Specifies the first glyph. Specifies the number of glyphs. Specifies a starting display list. This function creates count display lists in the current Open. GL rendering context. Each display list consists of a single call to gl. Bitmap. Display list. Base+i corresponds to glyph first+i of the font currently selected in the device context specified by hdc, i = 0, 1, 2, . . . , count 1.

BOOL wgl. Use. Font. Outlines(HDC hdc, DWORD first, DWORD count, DWORD list. Base, FLOAT deviation, FLOAT extrusion, int format, LPGLYPHMETRICSFLOAT lpgmf) hdc: first: count: list. Base: deviation: extrusion: format: lpgmf : Specifies the device context with the desired outline font. Specifies the first glyph. Specifies the number of glyphs. Specifies a starting display list. Specifies the maximum chordal deviation from the original outlines. Specifies how much a font is extruded in the negative z direction. WGL_FONT_LINES or WGL_FONT_POLYGONS. Points to an array of GLYPHMETRICSFLOAT structures that is to receive the metrics of the glyphs. When lpgmf is NULL, no glyph metrics are returned. This function creates count display lists in the current Open. GL rendering context. Display list. Base+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. Open. GL does not support reading images from or saving images to files. System Memory Unpack Texture Memory Pack Pixel Storage Modes Frame Buffer Fragment Operations Pixel Transfer Operations (Pixel Map) Rasterization (Pixel Zoom)

Reading, Writing and Copying Pixel Data Reading Pixel Data from Frame Buffer to System Memory Unpack Texture Memory Pack Pixel Storage Modes Frame Buffer Fragment Operations Pixel Transfer Operations (Pixel Map) Rasterization (Pixel Zoom)

void gl. Read. Pixels( 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 rectangle width, height: Width and height of the frame buffer rectangle format: Pixel data elements to be read type: Data type of each pixel data element pixels: System memory to receive pixel data Pixel data element formats 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 (continued) 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 GL_BGR and GL_BGRA pixel formats were added in Open. GL 1. 2.

Normal data types for pixel data element 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 Each element is scaled to fit the range of the specified data type.

Packed data types for pixel data element (added in Open. GL 1. 2) 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_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 packed unsigned 32 -bit integer GL_UNSIGNED_INT_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

Valid pixel element formats for packed data types 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_REV GL_RGB GL_UNSIGNED_SHORT_4_4 GL_RGBA, GL_BGRA GL_UNSIGNED_SHORT_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_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

Example of packed data types: GL_UNSIGNED_BYTE_3_3_2 with GL_RGB Red 7 6 Green 5 4 3 Blue 2 1 0 GL_UNSIGNED_BYTE_2_3_3_REV with GL_RGB Blue 7 6 Green 5 4 Red 3 2 1 0

GL_UNSIGNED_SHORT_4_4 with GL_RGBA Red Green 15 14 13 12 11 10 9 Blue 8 7 6 5 Alpha 4 3 2 1 0 GL_UNSIGNED_SHORT_4_4 with GL_BGRA Blue Green 15 14 13 12 11 10 9 Red 8 7 6 5 Alpha 4 3 2 1 0 GL_UNSIGNED_SHORT_4_4_REV with GL_RGBA Alpha Blue 15 14 13 12 11 10 9 Green 8 7 6 5 Red 4 3 2 1 0 GL_UNSIGNED_SHORT_4_4_REV with GL_BGRA Alpha Red 15 14 13 12 11 10 9 Green 8 7 6 5 Blue 4 3 2 1 0

Writing Pixel Data from System Memory to Frame Buffer System Memory Unpack Texture Memory Pack Pixel Storage Modes Frame Buffer Fragment Operations Pixel Transfer Operations (Pixel Map) Rasterization (Pixel Zoom)

void gl. Draw. Pixels( 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 rectangle format: Pixel data elements to be written type: Data type of each pixel data element pixels: System memory that stores the pixel data format and type have the same meaning as with gl. Read. Pixels().

Copying Pixel Data inside Frame Buffer System Memory Unpack Texture Memory Pack Pixel Storage Modes Frame Buffer Fragment Operations Pixel Transfer Operations (Pixel Map) Rasterization (Pixel Zoom)

void gl. Copy. Pixels( 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 rectangle width, height: Width and height of the pixel rectangle buffer: GL_COLOR, GL_STENCIL, GL_DEPTH Note: gl. Copy. Pixels() does not need data format or type information and it is not affected by pixel storage modes.

Pixel Storage Modes System Memory Unpack Pixel Storage Modes Packing: Unpacking: Texture Memory Frame Buffer Fragment Operations Pixel Transfer Operations (Pixel Map) Rasterization (Pixel Zoom) The way in which pixel data is written to system memory. The way in which pixel data is read from system memory. void gl. Pixel. Storei(GLenum pname, GLint param) void gl. Pixel. Storef(GLenum pname, GLfloat param) Set pixel storage modes. pname: parameter name. param: parameter value.

Parameter name Type Initial value Valid range GL_UNPACK_ALIGNMENT GL_PACK_ALIGNMENT GLint 4 1, 2, 4, 8 GL_UNPACK_SWAP_BYTES GL_PACK_SWAP_BYTES GLboolean GL_FALSE GL_TRUE, GL_FALSE GL_UNPACK_LSB_FIRST GL_PACK_LSB_FIRST GLboolean GL_FALSE GL_TRUE, GL_FALSE GL_UNPACK_ROW_LENGTH GL_PACK_ROW_LENGTH GLint 0 non-negative integer GL_UNPACK_SKIP_ROWS GL_PACK_SKIP_ROWS GLint 0 non-negative integer GL_UNPACK_SKIP_PIXELS GL_PACK_SKIP_PIXELS GLint 0 non-negative integer 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 memory 2: Data is aligned on 16 -bit address boundary in system memory 4: Data is aligned on 32 -bit address boundary in system memory 8: 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. *ROW_LENGTH Sub-Image *SKIP_PIXELS *SKIP_ROWS Image

Pixel Transfer Operations Pixel transfer operations perform conversions on pixel data. void gl. Pixel. Transferi(GLenum pname, GLint param) void gl. Pixel. Transferf(GLenum pname, GLfloat param) void gl. Pixel. Mapuiv(GLenum map, GLint size, const GLuint *values) void gl. Pixel. Mapusv(GLenum map, GLint size, const GLushort *values) void gl. Pixel. Mapfv(GLenum map, GLint size, const GLfloat *values)

Pixel Zoom void gl. Pixel. Zoom(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.