CS 470 Introduction to Computer Graphics

CS 470Introduction toComputer Graphics Bitmaps & Images

Bitmaps and Images • Some objects that we might draw are not geometry • These objects are images and consist of bitmaps • You can’t (for the most part) manipulate bitmaps the same way you manipulate geometry.

Bitmaps and Images • OpenGL pipeline Geometry Rasterization Display Bitmaps/ Pixels

Bitmaps and Images void glBitmap(GLsizei r, GLsize c, GLfloat dx, GLfloat dy, GLfloat xn, GLfloat yn, GLubyte *array); Creates an r by c image from the bitmap array located at dx, dy from the current raster position. xn, yn are the new values of rasterposition.

Bitmaps and Images • Sample code – GLubyte wb[2] = {0x00, 0xff}; GLubyte check[512]; int i, j; for[i=0; i<64, i++) for (j=0; j<8, j++); check[i*8 +j] = wb[(i/8+j)%2]; glBitmap(64, 64, 0.0, 0.0, 0.0, 0.0, check); from Angel, 2002

Bitmaps and Images void glLogicOp(Glenum logop); Determines the logicial operation used to display the image over existing display. Default is to replace the existing pixel with the image pixel Must enable with glEnable(GL_COLOR_LOGIC_OP);

Bitmaps and Images • Some logic operations • GL_CLEAR • GL_COPY source • GL_NOOP destination • GL_SET set regardless • GL_OR s OR d • GL_XOR s XOR d

Bitmaps and Images void glDrawPixels(GLsizei w, GLsizei h, GLenum format, GLenum type, void *array); Draws images from pixels defined in array at current raster position. Format can be GL_RGB, GL_RGBA, GL_RED, …, GL_DEPTH_COMPONENT

Bitmaps and Images void glReadPixels(GLint x, GLsize y, GLsize w, GLsize h, GLenum format, GLenum type, void *array); Takes a snapshot of a w by h rectangle at x, y and stores it in an array;

Bitmaps and Images void glCopyPixels(GLint x, GLint y, GLsizei w, GLsizei h, GLenum buffer); copies a w by h rectangular image from buffer at x, y and puts it at current raster position.

Bitmaps and Pixels void glReadBuffer(GLenum buffer); void glDrawBuffer(GLenum buffer); Determines the buffer used for reading or drawing respectively.

Bitmaps and Images • Buffers can be • GL_FRONT • GL_BACK • GL_FRONT_AND_BACK • GL_RIGHT_FRONT • GL_LEFT_FRONT • GL_RIGHT_FRONT • GL_LEFT_FRONT • …

Bitmaps and Images • Pixel mapping • alters pixel values according to a map • allows you to make color adjustments • allows you to create false colors

Bitmaps and Images void glPixelTransfer{i|f}(GLenum name, Type value); Defines how pixel mapping can occur i.e. – glPixelTransferi(GL_MAP_COLOR, GL_TRUE);

Bitmaps and Images void glPixelMap{us|ui|f}v(GLenum map, GLint size, TYPE *array); Defines a map for translating pixel to new pixel values. Map can be GL_PIXEL_MAP_I_TO_R {G|B} or …R_TO_R, B_TO_B, G_TO_G

Bitmaps and Images void glPixelZoom(GLfloat sx, sy); scales pixels in bitmap by factors sx and sy. sx, sy > 1 – enlarge sx,sy < 1 – reduce negative sx, sy invert the image

Bitmaps and Images void gluScaleImage(GLenum format, GLint win, GLint hin, GLenum typein, void *imagein, GLint wout, GLint hout, GLenum typeout, void *imageout); Scales an image/bitmap from imagein and writes it to imageout.

Bitmaps and Images • Image processing

CS 470 Introduction to Computer Graphics