Hi all,
Those of you who read my preious post yesterday on this same subject know what a predicament I was in. I just though I''d just follow up and pass on what I learned. As it turns out, I was finally able to solve my problem with superimposing 2D text and interface over a 3D scene. Although I can proudly say that I managed to solve this, the help of the veterans here, especially Davepermen and Zedzeke got me started in the right direction
Fellow newbies, what I''m about to write may have some errors or misconceptions. I don''t want to lead anyone astray. I would like to try to give back to the community here at least a little of what was given me
Veterans, hope you''ll correct any mistakes I''ve made here
The problem boiled down to 2 things basically. 1: some confusion on my part on how class constructors initialize objects, and 2: fundamental lack of understanding concerning the various transformations and their matrix stacks.
I''ll repost the faulty code from yesterday here:
GLvoid CInterface::DrawInterface()
{
glPushMatrix();
glLoadIdentity();
glOrtho(0.0f, 640, 480, 0.0f, -1.0f, 1.0f);
PrintText(180, 20, "OpenGL Text -%7.2f", txtcnt1);
glPopMatrix();
}
GLvoid CInterface:rintText(GLint x, GLint y, const char *fmt, ...)
{
char text[256];
va_list ap;
if (fmt == NULL)
return;
va_start(ap, fmt);
vsprintf(text, fmt, ap);
va_end(ap);
glTranslated(x,y,0);
glListBase(fontset - 32);
glCallLists(strlen(text), GL_UNSIGNED_BYTE, text);
}
The first thing I had to do was move my CInterface::SetData() (not shown here, sorry
call out of CInterface''s constructor because it wasn''t being called at all. This is the function that initializes my fontset. I''m still not sure why this had to be done, because I''ve used my constructors to initialize other objects in a similar fashion without problems. Anyway once I did that, the text appeared to the screen but instead of stationary, it was zigzagging across the bottom of the screen. Almost as if it was being drawn to a different point with each rendering pass.
The problem here of course was due to my misunderstadning of the transformation matrices.
Originally, I had thought I could simply call PushMatrix() and PopMatrix() and everything would be hunky dorey. Not so!
Davepermen pointed out that I needed to call glMatrixMode() to switch to the projection matrix at the front and the call it again at the back to switch back to modelview matrix. This defintely got me thinking on the right track.
What I didn''t realize was that each transformation has it''s own seperate matrix stack. I had naively assumed that calling PushMatrix() and PopMatrix() applied to all the transformations. Instead, I found out that you have to call successive Push and PopMatrix() for each tranformation that you are working with.
So, the final, fully functioning code is like this:
GLvoid CInterface:
rintText(const char *fmt, ...)
{
char text[256];
va_list ap;
if (fmt == NULL)
return;
va_start(ap, fmt);
vsprintf(text, fmt, ap);
va_end(ap);
glListBase(fontset - 32);
glCallLists(strlen(text), GL_UNSIGNED_BYTE, text);
}
GLvoid CInterface::DrawInterface() //switch to 2D for drawing, then switch back to 3D
{
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glOrtho(0.0f, 640, 480, 0.0f, -1.0f, 1.0f);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
glColor3f(1.0f, 1.0f, 1.0f);
glRasterPos2i(20,20);
PrintText("OpenGL Text");
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
}
You''ll notice that switched from glTranslated() to glRasterPos2i() That was more a matter of taste than anything I guess.
Anyway, I know I''ve taken up enough message space. Hope somebody found something useful here
Brad
