Working Style of Program

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Cody Carson
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1 Table of Contents Working Style of Program...2 Linked List &Drawing Function...2 Selection Array...4 Buffer...5 Popup Menu...6 User Guide...7 Drawing an Item...7 Moving Item and Changing Color...8 Delete Object and Zoom...8 Undo...9 Summary...9

2 Working Style of Program Linked List &Drawing Function We have a linked list structure and a pointer linked to that list, named as head and defined as global variable. We will call head linked list to the linked list which is being to draw objects starting from here. Structure of these linked objects can be seen below. struct myobjectlist enum myshape type; /* type/shape of the object */ GLint name; /* used in selection matrix to identify object */ GLint col[3]; /* color array */ GLfloat pos[2]; /* position array in x-y domain*/ GLfloat bnd[2]; /* bound array in x-y domain */ GLfloat angle; struct myobjectlist *next; /* next object*/ } ; int struct myobjectlist *previous; /* previous object */ When there is a new item to draw, new object is created with following function and inserted into head linked list. createnewnode(struct myobjectlist **currentref) static int name = 0; struct myobjectlist *newnode = (struct myobjectlist *) malloc(sizeof(struct myobjectlist)); /* check if there is enough memory */ if(!newnode) return EXIT_FAILURE; Drawing function takes head global pointer and gets the first object of head linked list, then draws to the screen objects in an order starting from the first to last. int drawfunc(struct myobjectlist *obj, GLenum mode) if(!obj) return EXIT_FAILURE; while(obj->previous) obj = obj->previous;

Drawing to screen works dependent to type of object in drawing function as seen below. switch(obj->type) case MENU_LINE: gllinewidth(5); glbegin(gl_line); glvertex2f(0.0f, 0.

3 Drawing to screen works dependent to type of object in drawing function as seen below. switch(obj->type) case MENU_LINE: gllinewidth(5); glbegin(gl_line); glvertex2f(0.0f, 0.0f); glvertex2f(obj->bnd[0], obj->bnd[1]); glend(); gllinewidth(1); break; case MENU_BOX: glrectf(0.0f,0.0f,obj->bnd[0], obj->bnd[1]); break; All these types defined as enumeration in util.h file before. enum myshape MENU_LINE, MENU_BOX, MENU_TRIANGLE, MENU_SPHERE }; Illustration 1: Basic Functions

4 Selection Array Selection array is created when picking occurs in mouse callback function when it is triggered with mouse left button. As soon as selection array is created, it can be compared to viewport array (array which has been draw to screen) to get matching points. Pick creates selection array, compares it with viewport array and returns the name of selected items. In our example it returns the one on the top of selected items (You can select more than one item at once, but just the one on the top will be picked). GLuint pickfunc(int x, int y) glgetintegerv (GL_VIEWPORT, viewport); glselectbuffer (SELECT_BUFSIZE, selectbuf); (void) glrendermode (GL_SELECT); glmatrixmode (GL_PROJECTION); glpushmatrix (); glloadidentity (); /* create 5x5 pixel picking region near cursor location */ glupickmatrix ((GLdouble) x, (GLdouble) (viewport[3] - y), 5.0, 5.0, viewport); gluortho2d(0.0, WINDOW_W, 0.0, WINDOW_H); /* draw function */ drawfunc(head,gl_select); glmatrixmode (GL_PROJECTION); glpopmatrix (); glutswapbuffers(); glmatrixmode(gl_modelview); hits = glrendermode (GL_RENDER); if(hits!= 0) for (i = 0; i < hits; i++) /* for each hit */ selected = selectbuf[3+4*i]; } } } return selected;

5 Undo Buffer At every move a copy of head list that we mentioned before is stored in a cell of buffer. This buffer is a kind of FIFO (first in first out) stack and defined as global variable with a fixed size. Push and pop functions are being used to manipulate and use this buffer to provide undo functionality. int pushtobuffer(struct myobjectlist *head, struct myobjectlist **buffer, int *index) if(*index<0) return EXIT_FAILURE; int popfrombuffer(struct myobjectlist **headref, struct myobjectlist **buffer, int *index) if(*index == 0) return EXIT_FAILURE; When undo occours a copy of head stored in the top of buffer is moved to head linked list and previous state of the objects are retrieved. case MENU_UNDO: popfrombuffer(&head, buffer, &bufferindex); glutpostredisplay(); break;

6 Popup Menu Glut's popup menu feature is bounded to mouse right button. Initialization of the popup menu can be seen below. Each choice group is being attached as a submenu. void createpopupmenu(void) shapes = glutcreatemenu(shapemenuselect); glutaddmenuentry("line", MENU_LINE); glutaddmenuentry("square", MENU_BOX); glutaddmenuentry("triangle", MENU_TRIANGLE); glutaddmenuentry("sphere", MENU_SPHERE); colors = glutcreatemenu(colormenuselect); glutaddmenuentry("dark", MENU_DARK); glutaddmenuentry("red", MENU_RED); glutaddmenuentry("green", MENU_GREEN); glutaddmenuentry("yellow", MENU_YELLOW); glutaddmenuentry("blue", MENU_BLUE); mainmenu = glutcreatemenu(mainmenuselect); glutaddsubmenu("shape", shapes); glutaddsubmenu("color", colors); glutaddmenuentry("new_item", MENU_ITEM); glutaddmenuentry("undo", MENU_UNDO); glutaddmenuentry("exit!", MENU_EXIT); } glutattachmenu(glut_right_button);

7 User Guide Drawing an Item 1. Right click with mouse on free space. 2. Left click with mouse on New_Item to create a new object. 3. Define color and shape. (Not needed to draw, dark and line are default values) 4. Then left click with mouse on free space to specify start point and hold then drag cursor to boundary point of item that you want to draw. Illustration 2: Popup Menu Moving Item and Changing Color 1. Simply left click on and item and hold left button and drag where you want to drag the item. 2. To change the color of the item, click on a item and reselect color using pop up menu. Illustration 3: Changing Color of Left Eye

8 Delete Object and Zoom 1. Simply select item with left click with mouse and press 'D' button of keyboard to delete item. 2. Zoom in with 'Z' button and Zoom out with 'X' button. Reset zoom with 'C' button. Undo 1. Basicly click on 'UNDO' button that you have with pop up menu. Last 256 move that you made stored in undo buffer. So feel free to choose undo. Summary Program have been written with great effort to make user comfortable and to be informative for developers. I have followed look & feel principles in most ways and made an advanced sample of selection array to make it possible. I hope you will find the code useful in your opengl learning path.

12. Selection. - The objects selected are specified by hit records in the selection buffer. E.R. Bachmann & P.L. McDowell MV 4202 Page 1 of 13

12. Selection. - The objects selected are specified by hit records in the selection buffer. E.R. Bachmann & P.L. McDowell MV 4202 Page 1 of 13 12. Selection Picking is a method of capturing mouse clicks at some window position and determining what objects are beneath it. The basic idea is to enter the selection rendering mode with a small viewing