I'm trying to draw in OpenGL 2 vectors with a given angle (in radians) between them, something like this:
I managed to draw the vectors but I'm not sure how to place them at the specific angle:
glBegin(GL_LINES); // Vx
glColor4f(1, .5, 0, 1);
glVertex3f(0, 0, 0);
glVertex3f(0, vectorYRScalingValue, 0); // vectorYRScalingValue is 5.0
glEnd();
glBegin(GL_LINES); // Vy
glColor4f(1, .5, 0, 1);
glVertex3f(0, 0, 0);
glVertex3f(0, vectorYRScalingValue, 0);
glEnd();
If β is the angle to be rotated in radians.
We rotate this vector anticlockwise around the origin.
float c = cos(β);
float s = sin(β);
NewX = x * c - y * s;
NewY = x * s + y * c;
Related
I draw many lines to form a grid. I want to see the grid rotated on its X-axis, but I never get the intended result. I tried glRotatef and gluLookAt which does not work the way I want. Please see the pictures below.
this is the grid
this is how I want to see it
Edit: geez, posting the code here is also hard, lol, anyway here it is.
Edit2: removed, only leave the code that has issues.
Please find the code below, no matter how I set the gluLookAt, the grid result won't be in the perspective I want.
#include <GL/glut.h>
void display() {
...
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_LINES);
for (int i = 0; i < 720; i += 3)
{
glColor3f(0, 1, 1);
glVertex3f(linePoints[i], linePoints[i + 1], linePoints[i + 2]);
}
glEnd();
glFlush();
}
void init() {
glClearColor(0.0, 0.0, 0.0, 1.0);
glColor3f(1.0, 1.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, 4.0 / 3.0, 1, 40);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, -2, 1.25, 0, 0, 0, 0, 1, 0);
}
Lets assume, that you have a grid in the xy plane of the world:
glColor3f(0, 1, 1);
glBegin(GL_LINES);
for (int i = 0; i <= 10; i ++)
{
// horizontal
glVertex3f(-50.0f + i*10.0f, -50.0f, 0.0f);
glVertex3f(-50.0f + i*10.0f, 50.0f, 0.0f);
// vertical
glVertex3f(-50.0f, -50.0f + i*10.0f, 0.0f);
glVertex3f( 50.0f, -50.0f + i*10.0f, 0.0f);
}
glEnd();
Ensure that the distance of to the far plane of the projection is large enough (see gluPerspective). All the geometry which is not in between the near an far plane of the Viewing frustum is clipped.
Further more ensure that the aspect ratio (4.0 / 3.0) match the ratio of the viewport rectangle (window).
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, 4.0 / 3.0, 1, 200);
For the use of gluLookAt, the up vector of the view has to be perpendicular to the grid. If the grid is arranged parallel to the xy plane, then the up vector is z axis (0, 0, 1).
The target (center) is the center of the grid (0, 0, 0).
The point of view (eye position) is ought to be above and in front of the grid, for instance (0, -55, 50). Note the point of view is used for a grid with the bottom left of (-50, -50, 0) and a top right of (50, 50, 0).
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0, -55.0, 50.0, 0, 0, 0, 0, 0, 1);
i want to move an object along a path (sine wave), lets suppose object is a roller coaster.
it moves through translate but my problem is that i also want to rotate that object according to the path.
i tried this code before translate but its not working.
if (x = -4.8)
{
glRotatef(89, 1, 1, 0);
}
my code with only translation looks like this.
i want to add rotation here along sine waves
void object()
{ glPushMatrix();
glTranslatef(x, y, 0);
glColor3f(0.0f, 0.0f, 0.0f);//Set drawing color
glBegin(GL_QUADS);
glVertex2f(-0.3, 0.1);
glVertex2f(0.3, 0.1);
glVertex2f(0.3, -0.1);
glVertex2f(-0.3, -0.1);
glEnd();
glFlush();
glPopMatrix();
glFlush();
}
void drawsine()
{
glBegin(GL_LINE_STRIP);//Primitive
glColor3f(255, 0, 0);//Set drawing color
int i = 0;
float x = 0, y = 0;
for (x = -5; x < 6; x = x + 0.1)
{
y = (sin(3.142*x)) / 3.142*x;
glVertex2f(x, y);
//int j= 0;
sinex[i] = x;
siney[i] = y;
i++;
}
glEnd();
glFlush();
}
The angle of rotation depends on the direction vector along the sine wave.
The direction vector can be calculated by the subtraction of 2 positions. Subtract the position before the current position from the positions after the current position, to calcaulte the direction vector. In the following i is the current position of the object:
dx = sinex[i+1] - sinex[i-1];
dy = siney[i+1] - siney[i-1];
The angle of rotation can be calculated by the arcus tangent using atan2, which returns an angle in radians:
float ang_rad = atan2( dy, dx );
Since the angle has to be passed to glRotatef in degrees, the angle has to be converted from radians to degrees, before a rotation around the z axis can be performed.
A full circle in has 360 degrees or 2*Pi radians. So the scale from radians to degrees 180/Pi:
float ang_deg = ang_rad * 180.0f / M_PI;
glRotatef( ang_deg, 0, 0, 1 );
The following cde snippet show how to apply the code. Be aware that there is no bounds check. This means i has to be grater or equal 1 and less than the number of points - 1 (1 <= i < 110):
#define _USE_MATH_DEFINES
#include <math.h>
{
// [...]
drawsine();
x = sinex[i];
y = siney[i];
dx = sinex[i+1] - sinex[i-1];
dy = siney[i+1] - siney[i-1];
object();
// [...]
}
void object()
{
glPushMatrix();
glTranslatef(x, y, 0);
float ang_rad = atan2( dy, dx );
float ang_deg = ang_rad * 180.0f / M_PI;
glRotatef( ang_deg, 0, 0, 1 );
glColor3f(0.0f, 0.0f, 0.0f);
glBegin(GL_QUADS);
glVertex2f(-0.3, 0.1);
glVertex2f(0.3, 0.1);
glVertex2f(0.3, -0.1);
glVertex2f(-0.3, -0.1);
glEnd();
glPopMatrix();
}
I am trying to render a rectangle onto the screen. When the program is run, only the clear color shows up, and no rectangle.
Here's the code:
glClearColor(0.0, 0.0, 0.0, 0.0);
glViewport(0, 0, 1280, 720);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 1280, 720, 0, -10, 10);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClear(GL_COLOR_BUFFER_BIT || GL_DEPTH_BUFFER_BIT); //Clear the screen and depth buffer
int x = 100;
int y = 100;
while (!glfwWindowShouldClose(window)) {
glfwPollEvents();
glBegin(GL_QUADS);
glVertex2f(x, y);
glVertex2f(x + 10, y);
glVertex2f(x + 10, y + 10);
glVertex2f(x, y + 10);
glEnd();
gsm->update();
gsm->render();
glfwSwapBuffers(window);
}
It got culled. You had inverted Y axis with your projection, by supplying bottom =720 larger than top 0. Your quad is counterclockwise in your local coordinates, but in normalized coordinates it is clockwise. Remember, projection matrix is a part of global transform matrix! Now, if that's default state, then out of those two winding directions
the GL_CCW is the actual one, it is considered "Front". By default OpenGL culls triangles with mode glCullFace(GL_BACK), and quad internally is considered as pair of triangles).
Either change order of vertices
glBegin(GL_QUADS);
glVertex2f(x, y);
glVertex2f(x, y + 10);
glVertex2f(x + 10, y + 10);
glVertex2f(x + 10, y);
glEnd();
or change culling mode to match left-handedness of your coordinate system or disable culling.
See also:
1. https://www.khronos.org/opengl/wiki/Viewing_and_Transformations
2. The answer to Is OpenGL coordinate system left-handed or right-handed?
I am having trouble rotating an ellipse in OpenGL. So, I have some code to draw an ellipse as follows:
glPushAttrib(GL_CURRENT_BIT);
glColor3f(1.0f, 0.0f, 0.0f);
glLineWidth(2.0);
glPushMatrix();
glTranslatef(0, 0, 0); // ellipse centre
glBegin(GL_LINE_LOOP);
float inc = (float) M_PI / 500.0;
for (GLfloat i = 0; i < M_PI * 2; i+=inc)
{
float x = cos(i) * 0.4;
float y = sin(i) * 0.4;
glVertex2f(x, y);
}
glEnd();
glPopMatrix();
glPopAttrib();
This produces a picture as so:
Now what I want to do is rotate this ellipse clockwise. So I added a glrotate in between but the result was not what I had expected.
So, I did something like:
glPushAttrib(GL_CURRENT_BIT);
glColor3f(1.0f, 0.0f, 0.0f);
glLineWidth(2.0);
glPushMatrix();
glTranslatef(0, 0, 0);
glRotatef(-90, 1, 1, 0);
glBegin(GL_LINE_LOOP);
float inc = (float) M_PI / 500.0;
for (GLfloat i = 0; i < M_PI * 2; i+=inc)
{
float x = cos(i) * 0.4;
float y = sin(i) * 0.4;
glVertex2f(x, y);
}
glEnd();
glPopMatrix();
glPopAttrib();
This produced an image which was simply collapsed. What I wanted to do was rotate the ellipse along its center by the specified degrees. Also, I tried playing around with the various parameters of glRotatef but could not get it do as I expected. The resulting image looks like:
You're working in the XY plane, so you can't really rotate around a vector in XY. Instead, you want to rotate along the unit Z axis (glRotate (angle, 0, 0, 1);). Imagine your screen being the XY coordinate system and the Z axis pointing inwards. What you want is to rotate around the Z axis, so your XY plane remains in the XY plane.
I am trying to make a tank game. I have successfully loaded an OBJ model, and calculated its bounding box for the model at the origin.
I am now trying to apply the transformations done to my model in the game logic to the original coordinates for the bounding box. For this, I grab the modelview matrix right before drawing my model, then multiply this matrix for the two vectors that define the BBox.
Here is the code that draws my tank:
void drawTank()
{
bBox = calcBBox(modelo, 1);
glPushMatrix();
glBindTexture(GL_TEXTURE_2D, texTank);
glScalef(0.2, 0.2, 0.2);
glTranslatef(posTank.x,posTank.y,posTank.z);
glRotatef(anguloTanque, 0, 1, 0); // rotate around Y (horizontal)
glRotatef(90, 0, 1, 0);
glRotatef(-90, 1, 0, 0);
glGetFloatv(GL_MODELVIEW_MATRIX, matrix);
glmDraw(modelo, GLM_TEXTURE | GLM_MATERIAL);
glColor3f(1,0,0);
drawBBox(bBox);
glPopMatrix();
}
With this snippet, my bbox is properly drawn over the tank model (transformations are applied in rendering by the glTranslate & glRotate functions). As you can see I also grab here my ModelView matrix.
Then I apply this matrix as follows (this is my entire display function):
void Display(void) {
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
camera();
glEnable(GL_TEXTURE_2D);
//glTranslatef(0,-40,150);
//PLANE
glBindTexture(GL_TEXTURE_2D, texArena);
glBegin(GL_POLYGON);
glTexCoord2f( 0.0f, 0.0f );
glVertex3f(-500, 0, -500);
glTexCoord2f( 5.0f, 5.0f );
glVertex3f(500, 0, -500);
glTexCoord2f(5.0f, 0.0f );
glVertex3f(500, 0, 500);
glTexCoord2f( 0.0f, 5.0f );
glVertex3f(-500, 0, 500);
glEnd();
drawTank();
glPopMatrix();
point3D max = bBox.max;
point3D min = bBox.min;
point3D resultMax;
point3D resultMin;
//Transformacion
multVectorByMatrix(matrix, max, resultMax);
multVectorByMatrix(matrix, min, resultMin);
bBox.max.x = resultMax.x; bBox.max.y = resultMax.y; bBox.max.z = resultMax.z;
bBox.min.x = resultMin.x; bBox.min.y = resultMin.y; bBox.min.z = resultMin.z;
glPushMatrix();
glColor3f(1,1,1);
drawBBox(bBox);
glPopMatrix();
glFlush();
glutSwapBuffers();
}
The function that multiplies a vector by a matrix:
void multVectorByMatrix(float* matrix, point3D vector, point3D &result)
{
result.x = (matrix[0] * vector.x) +
(matrix[4] * vector.y) +
(matrix[8] * vector.z) +
matrix[12];
result.y = (matrix[1] * vector.x) +
(matrix[5] * vector.y) +
(matrix[9] * vector.z) +
matrix[13];
result.z = (matrix[2] * vector.x) +
(matrix[6] * vector.y) +
(matrix[10] * vector.z) +
matrix[14];
}
If I draw the bounding box with this render loop, then my bounding box gets drawn but transformations are not applied properly. I can see the bounding box moving correctly with translations, but rotations are not done right.
What might be the problem here?
edit: some screenshots
Your problem is in this code.
point3D max = bBox.max;
point3D min = bBox.min;
point3D resultMax;
point3D resultMin;
//Transformacion
multVectorByMatrix(matrix, max, resultMax);
multVectorByMatrix(matrix, min, resultMin);
bBox.max.x = resultMax.x; bBox.max.y = resultMax.y; bBox.max.z = resultMax.z;
bBox.min.x = resultMin.x; bBox.min.y = resultMin.y; bBox.min.z = resultMin.z;
glPushMatrix();
glColor3f(1,1,1);
drawBBox(bBox);
glPopMatrix();
You take two vertices from your box and then apply transformations to them, then you use this transformed vertices to display a box, which of course will be axis aligned, because that's the only box you can get from just two opposite vertices. And you can see on your screenshot, that you bbox and the correct bbox have common vertices - these are exactly the vertices you applied your transformations to. So, in order to get a correct bbox, you need to get all vertices of the bbox and apply these transformations to all of them. Then you'll get exactly what you want.