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Weird Translations

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Started by adam_o December 11, 2006 08:55 PM

17 comments, last by adam_o 17 years, 4 months ago

adam_o

137

Author

December 11, 2006 10:26 PM

Quote:Original post by jyk
There are a couple of things in your code I'm not sure about, but I would try adding a call to glLoadIdentity() before the line:
glTranslatef(0.0, 0.0, ztrans);
As it is now, you're accumulating the translation from frame to frame in the OpenGL modelview matrix, which is not what you want.

So in the "kybrd" function I should put something like:

void kybrd(unsigned char key, int x, int y){	switch (key)	{		case 'w':		{			ztrans = 0.1;			glutPostRedisplay();			break;		}		case 'x':		{			ztrans = -0.1;			glutPostRedisplay();			break;		}		case 27:		{			exit(0);			return;		}		default: return;	}}

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Zakwayda

2,389

December 11, 2006 11:44 PM

Quote:Original post by adam_o
Quote:Original post by jyk
There are a couple of things in your code I'm not sure about, but I would try adding a call to glLoadIdentity() before the line:
glTranslatef(0.0, 0.0, ztrans);
As it is now, you're accumulating the translation from frame to frame in the OpenGL modelview matrix, which is not what you want.
So in the "kybrd" function I should put something like:

*** Source Snippet Removed ***

That should have more or less the same effect, but in general it's better to manage incremental transforms on your end rather than having OpenGL do it.

As such, the function was fine as it was before. I would instead recommend adding glLoadIdentity() as described in my previous post.

Zahlman

1,682

December 12, 2006 06:16 AM

Cleaned up a bit:

#include <GLUT/glut.h>#include <string>#include <sstream>using namespace std;GLfloat ztrans;void drawString(GLint x, GLint y, const string& s) {	glPushAttrib(GL_TRANSFORM_BIT | GL_CURRENT_BIT);	glMatrixMode(GL_PROJECTION);	glPushMatrix();	glLoadIdentity();	glOrtho(0, 640, 0, 480, -10.0, 10.0);	glMatrixMode(GL_MODELVIEW);	glPushMatrix();	glLoadIdentity();	glColor4f(1.0, 1.0, 1.0, 1.0);	glRasterPos2i(x, y);	for (string::iterator it = s.begin(); it != s.end(); ++it) 	{		glutBitmapCharacter(GLUT_BITMAP_8_BY_13, *it);	}	glPopMatrix();	glMatrixMode(GL_PROJECTION);	glPopMatrix();	glPopAttrib();}void draw(){	glTranslatef(0.0, 0.0, ztrans);	glClear(GL_COLOR_BUFFER_BIT);	glBegin(GL_QUADS);	glVertex3f(0.0, 0.0, -5.0);	glVertex3f(1.0, 0.0, -5.0);	glVertex3f(1.0, 1.0, -5.0);	glVertex3f(0.0, 1.0, -5.0);	glEnd();	stringstream ss("Keys are 'w', 'x' or ESC to exit, ztrans = ");	ss << ztrans;	drawString(10, 10, ss.str());	glFlush();}void init(){	glClearColor(0.0, 0.0, 0.0, 0.0);	glMatrixMode(GL_PROJECTION);	glLoadIdentity();	gluPerspective(100.0, 1.0, 0.001, 10000.0);	glMatrixMode(GL_MODELVIEW);}void handle_keyboard(unsigned char key, int, int){	switch (key)	{		case 'w':		{			ztrans += 0.1;			glutPostRedisplay();			break;		}		case 'x':		{			ztrans -= 0.1;			glutPostRedisplay();			break;		}		case 27:		{			exit(0);		}	}}int main(int argc, char** argv){	glutInit(&argc, argv);	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);	glutInitWindowSize(500, 500);	glutInitWindowPosition(100, 100);	glutCreateWindow("Weird Translations");	init();	glutKeyboardFunc(handle_keyboard);	glutDisplayFunc(draw);	glutMainLoop();}

adam_o

137

Author

December 12, 2006 07:23 PM

Quote:Original post by Zahlman
Cleaned up a bit:

*** Source Snippet Removed ***

Is there any way you could quickly comment to show what you fixed or just show where it is?

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Zahlman

1,682

December 12, 2006 09:42 PM

Functions are reorganized to remove the need for prototypes, and std::string is used for representing text (along with std::stringstream to accumulate text). Beyond that, nothing major.

adam_o

137

Author

December 13, 2006 05:51 PM

Quote:Original post by Zahlman
Functions are reorganized to remove the need for prototypes, and std::string is used for representing text (along with std::stringstream to accumulate text). Beyond that, nothing major.

ookk...

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adam_o

137

Author

December 13, 2006 10:39 PM

Ok, new question. My code creates a stretched box, but I told it to make a square. I know that gluPerspective() and glutInitWindowSize() effect the way this is stretched, but what numbers should I put in them?? I want to create a 1024 by 768 window, and my computer is 1280 by 854. I created four variables, as you will see below, that control this, two for my window size, two for the resolution of my screen.

int xdimension = 1024;int ydimension = 768;int realxdimension = 1280;int realydimension = 854;//...glutInitWindowSize(xdimension, ydimension);//...gluPerspective(100.0, realxdimension/realydimension, 0.001, 10000.0);

I hoped that this would work, but it doesn't. What gives?

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Zahlman

1,682

December 14, 2006 12:06 AM

Dividing two integers performs integer division (which discards the remainder). You are interested in the ratio as a floating-point value, so you must cast either or both to a floating-point type before performing the division.

adam_o

137

Author

December 14, 2006 06:24 PM

Quote:Original post by Zahlman
Dividing two integers performs integer division (which discards the remainder). You are interested in the ratio as a floating-point value, so you must cast either or both to a floating-point type before performing the division.

So I nead to make them floating point numbers (so I guess since I'm using OpenGL then GLfloat) to get it to work nicely?

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