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| GL_CULL_FACE and GL_FRONT_AND_BACK |
Author :
blotfib
Post Date :
2006-03-31 18:34
Posts :
9
|
Hi
I have pbs in converting some openGL code to ES one :
I need to draw a "trièdre" (i, j, k), a triangle with a unique color, a floor with just lines (in fact sqares not filled)
and a cube with texture.
The cube with texture is ok, the trièdre also.
but the lines on the floor do not apear also with my yellow triangle nothing visible...
here are the part of code:
GLfloat Reperexyz[] = {
0.0f,0.0f,0.0f,
0.1f,0.0f,0.0f,//x
0.0f,0.0f,0.0f,
0.0f,0.2f,0.0f,//y
0.0f,0.0f,0.0f,
0.0f,0.0f,0.3f,//z
};
GLfloat RepereTriangle[] = {
0.0f, 0.0f, -0.1f,
0.086f, 0.0f, 0.05f,
-0.086f, 0.0f, 0.05f,
};
GLfloat TerrainCarre[] = {
0.0f, 0.0f, 0.0f,
0.5f, 0.0f, 0.0f,
0.5f, 0.5f, 0.0f,
0.0f, 0.5f, 0.0f,
};
GLfloat box[] = {
// FRONT
-0.5f, -0.5f, 0.5f,
0.5f, -0.5f, 0.5f,
-0.5f, 0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
// BACK
-0.5f, -0.5f, -0.5f,
... (the box is the one of the tutorial, works well of course ;-)
void TGL_Form::DrawScene()
{
float deb=10.0;
int i, j, nbSubdiv=40; /* Nombre de subdivisions du maillage */
float pas=2.0*deb/nbSubdiv;
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glEnableClientState(GL_VERTEX_ARRAY);
glEnable(GL_CULL_FACE);
glShadeModel(GL_SMOOTH);
glTranslatef(0, 0, -zpos);
glRotatef(xrot,1,0,0);
//------- point de vision
// marque "en altitude ypos" du point de vision
glColor4f(1.0f,1.0f,0.0f,1.0f);
glPushMatrix ();
glScalef(zpos*0.5,zpos*0.5,zpos*0.5);
glNormal3f(0.0f, 0.0f, 1.0f);
glVertexPointer(3, GL_FLOAT, 0, RepereTriangle);
glDrawArrays(GL_TRIANGLES, 0, 3);
glPopMatrix ();
glTranslatef(0,-yv, 0);
// marque au sol de l'ombre du point de vision
glColor4f(0.4f,0.4f,0.4f,1.0f);
glPushMatrix ();
glScalef(zpos*0.5,zpos*0.5,zpos*0.5);
glDrawArrays(GL_TRIANGLES, 0, 3);
glPopMatrix ();
//------- fin point de vision
glRotatef(yrot,0,1,0);
glTranslatef(-xv, 0, -zv);
// affiche le terrain
// glDisable(GL_CULL_FACE);
glEnable(GL_CULL_FACE);
glCullFace(GL_FRONT_AND_BACK);
glPushMatrix ();
glRotatef (-(GLfloat)90.0, (GLfloat)1.0, (GLfloat)0.0, (GLfloat)0.0);
glColor4f(0.6,0.6,0.6, 1.0f);
// glLineWidth(1.0);
for (i=0;i<nbSubdiv;i++)
for (j=0;j<nbSubdiv;j++)
{
glPushMatrix ();
glTranslatef(-deb+i*pas, -deb+j*pas, 0.0f);
glVertexPointer(3, GL_FLOAT, 0, TerrainCarre);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glPopMatrix ();
}
glPopMatrix ();
glCullFace(GL_BACK);
glRotatef (-90.0, (GLfloat)1.0, (GLfloat)0.0, (GLfloat)0.0); // repere xy au sol !
glPushMatrix (); // dessine le cube UHP
glTranslatef(0.5f, 0, 0);
glRotatef (-90.0f, 1.0f, 0.0f, 0.0f); // retourne le cube et le déplace !
glScalef (0.3f, 0.3f, 0.3f); // rapetit
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glBindTexture(GL_TEXTURE_2D, texture1);
glVertexPointer(3, GL_FLOAT, 0, box);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords);
glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
// FRONT AND BACK
glNormal3f(0.0f, 0.0f, 1.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glNormal3f(0.0f, 0.0f, -1.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 4, 4);
// LEFT AND RIGHT
glBindTexture(GL_TEXTURE_2D, textureUHPGREEN);
glNormal3f(-1.0f, 0.0f, 0.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 8, 4);
glNormal3f(1.0f, 0.0f, 0.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 12, 4);
// TOP AND BOTTOM
glBindTexture(GL_TEXTURE_2D, textureUHP);
glNormal3f(0.0f, 1.0f, 0.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 16, 4);
glNormal3f(0.0f, -1.0f, 0.0f);
glDrawArrays(GL_TRIANGLE_STRIP, 20, 4);
glDisable(GL_TEXTURE_2D);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glPopMatrix ();
if (afficheRepere)
{
glLineWidth(2.0);
glColor4f(1.0,0.0,0.0,1.0f);
glVertexPointer(3, GL_FLOAT, 0, Reperexyz);
glDrawArrays(GL_LINES, 0, 2);
glColor4f(0.0,1.0,0.0,1.0f);
glDrawArrays(GL_LINES, 2, 2);
glColor4f(0.0,0.0,1.0,1.0f);
glDrawArrays(GL_LINES, 4, 2);
glLineWidth(1.0);
}
glFlush ();
glutSwapBuffers();
CalculateFrameRate();
UpDateStatusBar();
}
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Author :
blotfib
Post Date :
2006-03-31 19:31
Posts :
9
|
in fact, how to translate :
glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
and
glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
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Author :
blotfib
Post Date :
2006-03-31 20:37
Posts :
9
|
ok
I changed my way and now I am drawing lines :
glVertexPointer(3, GL_FLOAT, 0, TerrainCarre);
glDrawArrays(GL_LINE_LOOP, 0, 4);
works well, but I don't understand why we dont se the lines if it is :
glEnable(GL_CULL_FACE);
glCullFace(GL_FRONT_AND_BACK);
|
Author :
grant
Post Date :
2006-04-01 07:26
Posts :
117
|
Hi,
glCullFace is used to specify which faces are called. For example, if you pass GL_FRONT, front facing polygons will be culled.
If you pass GL_FRONT_AND_BACK, you are telling OpenGL ES to cull both front facing and back facing polygons which will in essence render nothing.
Generally you would leave the value of this function as the default which is GL_BACK.
Regards,
Grant |
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