tati987

08-06-2017, 11:37 AM

Hi,

I'm new to opengl, and trying to create a small project with it. I have created some kind of a floor on the x-y plane, and I want to be able to turn the camera with the arrows to look around.

I created an array for the camera position ([x,y,z] values) and an array for the direction of viewing which is added to the camera location to get the look at point. Both these parameters - the camera location and the look at should be able to receive any value (within the perspective), I want to be able to change them later as I want while the program is running.

At first I calculate the degree of the viewing direction with the x axis, and for every arrow key press I increase this degree by 0.01.

What I don't understand, is why when creating the rotation, I need to add 90 degrees to the starting angle. If I don't add the 90 degrees, the viewing direction is as expected, but when I press the arrow keys (which add the right values as seems), the rotation jumps 90 degrees back (clockwise) and then continues smoothly.

Can anyone help me with this?

My code:

#include <GL\glut.h>

#include <cmath>

#include <math.h>

double rotationAngle;

bool isPerspective;

double winSizeX;

double winSizeY;

bool rightMouseDown;

int mouseX;

int mouseY;

int deltaX;

int deltaY;

float currentViewDirection[3] = { 1, 1, 0 };

float currentCameraLocation[3] = { 0, 5, 5 };

const double PI = 3.141592653589793238463;

float xViewAngle;

void drawFloor(void) {

for (int row = -50; row <= 50; row++)

{

for (int col = -50; col <= 50; col++)

{

int colorNum = (abs(row) % 3) + (abs(col) % 3) - 1;

switch (colorNum)

{

case 0:

{

glColor3ub(254, 232, 178);

break;

}

case 1:

{

glColor3ub(79, 39, 0);

break;

}

case 2:

{

glColor3ub(168, 67, 0);

break;

}

}

glBegin(GL_POLYGON);

glVertex3d(row, col, 0);

glVertex3d(row + 1, col, 0);

glVertex3d(row + 1, col + 1, 0);

glVertex3d(row, col + 1, 0);

glEnd();

}

}

}

void display(void)

{

glMatrixMode(GL_MODELVIEW);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_MODELVIEW);

glLoadIdentity();

gluLookAt(currentCameraLocation[0], currentCameraLocation[1], currentCameraLocation[2],

currentCameraLocation[0] + currentViewDirection[0], currentCameraLocation[1] + currentViewDirection[1], currentCameraLocation[2] + currentViewDirection[2],

0, 0, 1);

drawFloor();

glutSwapBuffers();

}

void reshape(int x, int y) {

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

gluPerspective(60, (GLdouble)1200 / (GLdouble)900, 0.1f, 1000);

glViewport(0, 0, 1200, 900);

}

void specialInput(int key, int x, int y)

{

float vectorLength = sqrt(currentViewDirection[0] * currentViewDirection[0] + currentViewDirection[1] * currentViewDirection[1] + currentViewDirection[2] * currentViewDirection[2]);

switch (key)

{

case GLUT_KEY_LEFT:

{

xViewAngle -= 0.01f;

currentViewDirection[0] = -cos(xViewAngle) * vectorLength;

currentViewDirection[1] = sin(xViewAngle) * vectorLength;

break;

}

case GLUT_KEY_RIGHT:

{

xViewAngle += 0.01f;

currentViewDirection[0] = -cos(xViewAngle) * vectorLength;

currentViewDirection[1] = sin(xViewAngle) * vectorLength;

break;

}

}

}

int main(int argc, char **argv)

{

if (currentViewDirection[0] != 0) {

xViewAngle = atan(currentViewDirection[1] / currentViewDirection[0]);

}

else {

if (currentViewDirection[1] > 0) {

xViewAngle = PI/2;

}

else

{

xViewAngle = -PI/2;

}

}

// if this is removed, the rotation will jump at the beginning

xViewAngle += PI / 2;

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

glutInitWindowPosition(50, 50);

glutInitWindowSize(1200, 900);

glutCreateWindow("A");

glutDisplayFunc(display);

glutReshapeFunc(reshape);

glutIdleFunc(display);

glutSpecialFunc(specialInput);

glutMainLoop();

return 0;

}

I'm new to opengl, and trying to create a small project with it. I have created some kind of a floor on the x-y plane, and I want to be able to turn the camera with the arrows to look around.

I created an array for the camera position ([x,y,z] values) and an array for the direction of viewing which is added to the camera location to get the look at point. Both these parameters - the camera location and the look at should be able to receive any value (within the perspective), I want to be able to change them later as I want while the program is running.

At first I calculate the degree of the viewing direction with the x axis, and for every arrow key press I increase this degree by 0.01.

What I don't understand, is why when creating the rotation, I need to add 90 degrees to the starting angle. If I don't add the 90 degrees, the viewing direction is as expected, but when I press the arrow keys (which add the right values as seems), the rotation jumps 90 degrees back (clockwise) and then continues smoothly.

Can anyone help me with this?

My code:

#include <GL\glut.h>

#include <cmath>

#include <math.h>

double rotationAngle;

bool isPerspective;

double winSizeX;

double winSizeY;

bool rightMouseDown;

int mouseX;

int mouseY;

int deltaX;

int deltaY;

float currentViewDirection[3] = { 1, 1, 0 };

float currentCameraLocation[3] = { 0, 5, 5 };

const double PI = 3.141592653589793238463;

float xViewAngle;

void drawFloor(void) {

for (int row = -50; row <= 50; row++)

{

for (int col = -50; col <= 50; col++)

{

int colorNum = (abs(row) % 3) + (abs(col) % 3) - 1;

switch (colorNum)

{

case 0:

{

glColor3ub(254, 232, 178);

break;

}

case 1:

{

glColor3ub(79, 39, 0);

break;

}

case 2:

{

glColor3ub(168, 67, 0);

break;

}

}

glBegin(GL_POLYGON);

glVertex3d(row, col, 0);

glVertex3d(row + 1, col, 0);

glVertex3d(row + 1, col + 1, 0);

glVertex3d(row, col + 1, 0);

glEnd();

}

}

}

void display(void)

{

glMatrixMode(GL_MODELVIEW);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_MODELVIEW);

glLoadIdentity();

gluLookAt(currentCameraLocation[0], currentCameraLocation[1], currentCameraLocation[2],

currentCameraLocation[0] + currentViewDirection[0], currentCameraLocation[1] + currentViewDirection[1], currentCameraLocation[2] + currentViewDirection[2],

0, 0, 1);

drawFloor();

glutSwapBuffers();

}

void reshape(int x, int y) {

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

gluPerspective(60, (GLdouble)1200 / (GLdouble)900, 0.1f, 1000);

glViewport(0, 0, 1200, 900);

}

void specialInput(int key, int x, int y)

{

float vectorLength = sqrt(currentViewDirection[0] * currentViewDirection[0] + currentViewDirection[1] * currentViewDirection[1] + currentViewDirection[2] * currentViewDirection[2]);

switch (key)

{

case GLUT_KEY_LEFT:

{

xViewAngle -= 0.01f;

currentViewDirection[0] = -cos(xViewAngle) * vectorLength;

currentViewDirection[1] = sin(xViewAngle) * vectorLength;

break;

}

case GLUT_KEY_RIGHT:

{

xViewAngle += 0.01f;

currentViewDirection[0] = -cos(xViewAngle) * vectorLength;

currentViewDirection[1] = sin(xViewAngle) * vectorLength;

break;

}

}

}

int main(int argc, char **argv)

{

if (currentViewDirection[0] != 0) {

xViewAngle = atan(currentViewDirection[1] / currentViewDirection[0]);

}

else {

if (currentViewDirection[1] > 0) {

xViewAngle = PI/2;

}

else

{

xViewAngle = -PI/2;

}

}

// if this is removed, the rotation will jump at the beginning

xViewAngle += PI / 2;

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

glutInitWindowPosition(50, 50);

glutInitWindowSize(1200, 900);

glutCreateWindow("A");

glutDisplayFunc(display);

glutReshapeFunc(reshape);

glutIdleFunc(display);

glutSpecialFunc(specialInput);

glutMainLoop();

return 0;

}