人机接口与图形学(双语)12-OpenGL.ppt

Multiplication Order glMatrixMode (MODELVIEW); glLoadIdentity(); glMultMatrix(N); glMultMatrix(M); glMultMatrix(L); glBegin(POINTS); glVertex3f(v); glEnd(); Modelview matrix successively contains: I(dentity), N, NM, NML The transformed vertex is: NMLv = N(M(Lv)) Manipulating Matrix Stacks Observation: Certain model transformations are shared among many models We want to avoid continuously reloading the same sequence of transformations glPushMatrix ( ) push all matrices in current stack down one level and copy topmost matrix of stack glPopMatrix ( ) pop the top matrix off the stack Matrix Manipulation - Example Drawing a car with wheels and lugnuts draw_wheel( ); for (j=0; j5; j++) { glPushMatrix (); glRotatef(72.0*j, 0.0, 0.0, 1.0); glTranslatef (3.0, 0.0, 0.0); draw_bolt ( ); glPopMatrix ( ); } Matrix Manipulation - Example draw_wheel( ); for (j=0; j5; j++) { glPushMatrix (); glRotatef(72.0*j, 0.0, 0.0, 1.0); glTranslatef (3.0, 0.0, 0.0); draw_bolt ( ); glPopMatrix ( ); Global – Bottom Up Start Rot Trans Matrix Manipulation - Example draw_wheel( ); for (j=0; j5; j++) { glPushMatrix (); glRotatef(72.0*j, 0.0, 0.0, 1.0); glTranslatef (3.0, 0.0, 0.0); draw_bolt ( ); glPopMatrix ( ); Local – Top Down Start Rot Trans OpenGL: Conventions Functions in OpenGL start with gl Most functions just gl (e.g., glColor()) Functions starting with glu are utility functions (e.g., gluLookAt()) Functions starting with glx are for interfacing with the X Windows system (e.g., in gfx.c) OpenGL: Conventions Function names indicate argument type and number Functions ending with f take floats Functions ending with i take ints Functions ending with b take bytes Functions ending with ub take unsigned bytes Functions that end with v take an array. Examples glColor3f() takes 3 floats glColor4fv() takes an array of 4 floats OpenGL: Conventions Variables written in CAPITAL letters Example: GLUT_SINGLE, GLUT_RGB usually constants use the bitwise or command (x | y) to