how to make triangles visible from both sides
Author
OK so i'm making an icosahedron in this (well i have two triangles right now that don't really make a icosahedron) and i want to know how to make them visible on both sides. also if anyone has some insight on defining the correct triangles please say so.
Author
thanks a million!!!!!
o and i have already looked at that Wikipedia page but i cant seem to get the correct triangles even though i think i have the correct vertices (here's my code P1-P12 are vertices)
o and i have already looked at that Wikipedia page but i cant seem to get the correct triangles even though i think i have the correct vertices (here's my code P1-P12 are vertices)
#include <windows.h>#include <GL/glut.h>#include <GL/gl.h>#include <GL/glu.h>#include <stdlib.h>#include <stdio.h>#include <cmath>const GLfloat G_RATIO=(1.0f - sqrt(5.0f))/2.0f;GLfloat rtri;const GLfloat P1[] = {0.0f, 1.0f, G_RATIO};const GLfloat P2[] = {0.0f,-1.0f, G_RATIO};const GLfloat P3[] = { 0.0f,-1.0f, -G_RATIO};const GLfloat P4[] = {0.0f, 1.0f, -G_RATIO};const GLfloat P5[] = {1.0f,G_RATIO, 0.0f};const GLfloat P6[] = { -1.0f,G_RATIO, 0.0f};const GLfloat P7[] = { -1.0f, -G_RATIO, 0.0f};const GLfloat P8[] = {1.0f,-G_RATIO, 0.0f};const GLfloat P9[] = { G_RATIO,0.0f, 1.0f};const GLfloat P10[] = { -G_RATIO, 0.0f, 1.0f};const GLfloat P11[] = {-G_RATIO,0.0f, - 1.0f};const GLfloat P12[] = { G_RATIO,0.0f, -1.0f};static void resize(int width, int height){ const float ar = (float) width / (float) height; glDisable(GL_CULL_FACE); glEnable(GL_BLEND); glViewport(0, 0, width, height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glFrustum(-ar, ar, -1.0, 1.0, 2.0, 100.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity() ;}static void display(void){ const double t = glutGet(GLUT_ELAPSED_TIME) / 1000.0; const double a = t*90.0; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); glTranslatef(0.0f,0.0f,-5.0f); glRotatef(rtri,0.0f,1.0f,0.0f); glBegin(GL_TRIANGLES); glColor3f(1.0f,0.0f,0.0f); // Set Top Point Of Triangle To Red glVertex3fv( P5); // First Point Of The Triangle glColor3f(0.0f,1.0f,0.0f); // Set Left Point Of Triangle To Green glVertex3fv(P1); // Second Point Of The Triangle glColor3f(0.0f,0.0f,1.0f); // Set Right Point Of Triangle To Blue glVertex3fv( P4); glColor3f(1.0f,0.0f,0.0f); // Set Top Point Of Triangle To Red glVertex3fv( P6); // First Point Of The Triangle glColor3f(0.0f,1.0f,0.0f); // Set Left Point Of Triangle To Green glVertex3fv(P1); // Second Point Of The Triangle glColor3f(0.0f,0.0f,1.0f); // Set Right Point Of Triangle To Blue glVertex3fv( P12); glEnd(); rtri+=1.0f; glutSwapBuffers();}static void key(unsigned char key, int x, int y){ switch (key) { } glutPostRedisplay();}static void idle(void){ glutPostRedisplay();}const GLfloat light_ambient[] = { 0.0f, 0.0f, 0.0f, 1.0f };const GLfloat light_diffuse[] = { 1.0f, 1.0f, 1.0f, 1.0f };const GLfloat light_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };const GLfloat light_position[] = { 2.0f, 5.0f, 5.0f, 0.0f };const GLfloat mat_ambient[] = { 0.7f, 0.7f, 0.7f, 1.0f };const GLfloat mat_diffuse[] = { 0.8f, 0.8f, 0.8f, 1.0f };const GLfloat mat_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };const GLfloat high_shininess[] = { 100.0f };/* Program entry point */int main(int argc, char *argv[]){ glutInit(&argc, argv); glutInitWindowSize(640,480); glutInitWindowPosition(10,10); glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); glutCreateWindow("GLUT Shapes"); glutReshapeFunc(resize); glutDisplayFunc(display); glutKeyboardFunc(key); glutIdleFunc(idle); glClearColor(1,1,1,1); glEnable(GL_CULL_FACE); glCullFace(GL_BACK); glEnable(GL_DEPTH_TEST); glDepthFunc(GL_LESS); glEnable(GL_LIGHT0); glEnable(GL_NORMALIZE); glEnable(GL_COLOR_MATERIAL); glEnable(GL_LIGHTING); glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient); glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse); glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular); glLightfv(GL_LIGHT0, GL_POSITION, light_position); glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient); glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse); glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular); glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess); glutMainLoop(); return 1;}
Author
o and i would also like to know how to make it transparent with out using textures.
You are drawing 2 triangles...
anyway, I don't have time to look into it. Get a piece of paper and a pen, and start sketching...
anyway, I don't have time to look into it. Get a piece of paper and a pen, and start sketching...
Quote:Original post by ishkabible
o and i would also like to know how to make it transparent with out using textures.
glEnable(GL_BLEND) + glColor4f(r,g,b, alpha) where alpha = 1 means opaque and alpha = 0 means fully transparent.
Example:
...glColor4f(1.0f,0.0f,0.0f, 0.5f); // P5 will be red with 50% transparency.glVertex3fv( P5); ...You can change the blend equation with glBlendEquation and its factors with glBlendfunc but the default equation should be sufficient.
Edit: Note that in order to get correct results for alpha blended primitives you need to render them back to front, use additive blending (GL_ONE for both factors in glBlendFunc) which results in a brightening (might not be what you want) or use more advanced techniques like alpha-to-coverage (uses a texture) or depth peeling (uses render-to-texture).
Author
*nevermind i got it working, took some stuff that didn't need to be in my main and (here's a duzy) changed the colors so there wansn't just one color to display.
ok so i have this but it's just all one solid color not transparent at all so what did i do worng.
ok so i have this but it's just all one solid color not transparent at all so what did i do worng.
#include <windows.h>#include <GL/glut.h>#include <GL/gl.h>#include <GL/glu.h>#include <stdlib.h>#include <stdio.h>#include <cmath>const GLfloat G_RATIO = (1 - sqrt(5))/2;GLfloat rtri;const GLfloat P1[] = {0.0f, 1.0f, G_RATIO};const GLfloat P2[] = {0.0f,-1.0f, G_RATIO};const GLfloat P3[] = { 0.0f,-1.0f, -G_RATIO};const GLfloat P4[] = {0.0f, 1.0f, -G_RATIO};const GLfloat P5[] = {1.0f,G_RATIO, 0.0f};const GLfloat P6[] = { -1.0f,G_RATIO, 0.0f};const GLfloat P7[] = { -1.0f, -G_RATIO, 0.0f};const GLfloat P8[] = {1.0f,-G_RATIO, 0.0f};const GLfloat P9[] = { G_RATIO,0.0f, 1.0f};const GLfloat P10[] = { -G_RATIO, 0.0f, 1.0f};const GLfloat P11[] = {-G_RATIO,0.0f, - 1.0f};const GLfloat P12[] = { G_RATIO,0.0f, -1.0f};char *one;char *two;char *three;char *four;char *five;char *six;char *seven;char *eight;char *nine;char *ten;char *eleven;char *twelve;const GLfloat light_ambient[] = { 0.0f, 0.0f, 0.0f, 1.0f };const GLfloat light_diffuse[] = { 1.0f, 1.0f, 1.0f, 1.0f };const GLfloat light_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };const GLfloat light_position[] = { 2.0f, 5.0f, 5.0f, 0.0f };const GLfloat mat_ambient[] = { 0.7f, 0.7f, 0.7f, 1.0f };const GLfloat mat_diffuse[] = { 0.8f, 0.8f, 0.8f, 1.0f };const GLfloat mat_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };const GLfloat high_shininess[] = { 100.0f };static void resize(int width, int height){ const float ar = (float) width / (float) height; glDisable(GL_CULL_FACE); glEnable(GL_BLEND); glViewport(0, 0, width, height); glShadeModel(GL_SMOOTH); glLightfv(GL_LIGHT1, GL_AMBIENT, light_ambient); glLightfv(GL_LIGHT1, GL_DIFFUSE, light_diffuse); glLightfv(GL_LIGHT1, GL_SPECULAR, light_specular); glLightfv(GL_LIGHT1, GL_POSITION, light_position); glEnable(GL_LIGHT1); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glFrustum(-ar, ar, -1.0, 1.0, 2.0, 100.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity() ;}static void display(void){ const double t = glutGet(GLUT_ELAPSED_TIME) / 1000.0; const double a = t*90.0; one = "1"; two = "2"; three = "3"; four = "4"; five = "5"; six = "6"; seven = "7"; eight = "8"; nine = "9"; ten = "t"; eleven = "e"; twelve = "w"; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); glTranslatef(0.0f,0.0f,-5.0f); glRotatef(rtri,0.0f,1.0f,0.0f); glBegin(GL_TRIANGLES); glRasterPos3fv(P1); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *one); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P1); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P4); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P7); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P1); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P4); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P8); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P1); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P11); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P12); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P4); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P9); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P10); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P4); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P9); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P7); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P1); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P11); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P8); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P1); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P12); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P7); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P4); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P10); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P8); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P8); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P5); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P10); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P8); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P11); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P5); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P7); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P12); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P6); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P7); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P9); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P6); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P12); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P11); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P2); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P12); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P2); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P6); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P9); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P10); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P3); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P11); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P5); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P2); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P5); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P10); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P3); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P5); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P2); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P3); glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Top Point Of Triangle To Red glVertex3fv( P9); // First Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Left Point Of Triangle To Green glVertex3fv(P6); // Second Point Of The Triangle glColor4f(1.0f,0.0f,0.0f,0.5f); // Set Right Point Of Triangle To Blue glVertex3fv( P3); glEnd(); glRasterPos3fv(P1); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *one); glRasterPos3fv(P2); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *two); glRasterPos3fv(P3); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *three); glRasterPos3fv(P4); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *four); glRasterPos3fv(P5); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *five); glRasterPos3fv(P6); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *six); glRasterPos3fv(P7); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *seven); glRasterPos3fv(P8); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *eight); glRasterPos3fv(P9); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *nine); glRasterPos3fv(P10); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *ten); glRasterPos3fv(P11); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *eleven); glRasterPos3fv(P12); glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, *twelve); rtri+=1.0f; glutSwapBuffers();}void renderBitmapString( float x, float y, float z, void *font, char *string) { char *c; glRasterPos3f(x, y,z); for (c=string; *c != '\0'; c++) { glutBitmapCharacter(font, *c); }}static void key(unsigned char key, int x, int y){ switch (key) { } glutPostRedisplay();}static void idle(void){ glutPostRedisplay();}int main(int argc, char *argv[]){ glutInit(&argc, argv); glutInitWindowSize(640,480); glutInitWindowPosition(10,10); glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); glutCreateWindow("GLUT Shapes"); glutReshapeFunc(resize); glutDisplayFunc(display); glutKeyboardFunc(key); glutIdleFunc(idle); glClearColor(1,1,1,1); glEnable(GL_CULL_FACE); glCullFace(GL_BACK); glEnable(GL_DEPTH_TEST); glDepthFunc(GL_LESS); glEnable(GL_LIGHT0); glEnable(GL_NORMALIZE); glEnable(GL_COLOR_MATERIAL); glEnable(GL_LIGHTING); glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient); glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse); glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular); glLightfv(GL_LIGHT0, GL_POSITION, light_position); glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient); glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse); glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular); glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess); glutMainLoop(); return 1;}This topic is closed to new replies.
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