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;
Windows size : 640 * 480
Texture size : 1280 * 720
Hello, How can I scale the texture to the pygame window?
You've setup an orthographic projection:
glOrtho(0, self.windowWidth, self.windowHeight, 0, -1, 1)
If you want the texture to fill the whole window, then you have to draw a quad corresponding to the orthographic projection and the texture coordinates form (0, 0) to (1, 1):
glEnable(GL_TEXTURE_2D)
glBegin(GL_QUAD)
glTexCoord2f(0, 0)
glVertex2f(0, 0)
glTexCoord2f(1, 0)
glVertex2f(self.windowWidth, 0)
glTexCoord2f(1, 1)
glVertex2f(self.windowWidth, self.windowHeight)
glTexCoord2f(0, 1)
glVertex2f(0, self.windowHeight)
glEnd()
If you wan to keep the aspect ratio of the texture, then you have to scale the size of the quad. For instance:
left = 0
top = 0
width = self.windowWidth
height = self.windowHeight
sx = self.windowWidth / textureWidth
sy = self.windowHeight / textureHeight
if sx > sy:
width *= sy / sx
left = (self.windowWidth - width) / 2
else:
height *= sx / sy
top = (self.windowHeight - height) / 2
glEnable(GL_TEXTURE_2D)
glBegin(GL_QUAD)
glTexCoord2f(0, 0)
glVertex2f(left, top)
glTexCoord2f(1, 0)
glVertex2f(left + width, top)
glTexCoord2f(1, 1)
glVertex2f(left + width, top + height)
glTexCoord2f(0, 1)
glVertex2f(left, top + height)
glEnd()
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.
So I have this piece of code, which pretty much draws various 2D textures on the screen, though there are multiple sprites that have to be 'dissected' from the texture (spritesheet). The problem is that rotation is not working properly; while it rotates, it does not rotate on the center of the texture, which is what I am trying to do. I have narrowed it down to the translation being incorrect:
glTranslatef(x + sr->x/2 - sr->w/2,
y + sr->y/2 - sr->h/2,0);
glRotatef(ang,0,0,1.f);
glTranslatef(-x + -sr->x/2 - -sr->w/2,
-y + -sr->y/2 - -sr->h/2,0);
X and Y is the position that it's being drawn to, the sheet rect struct contains the position X and Y of the sprite being drawn from the texture, along with w and h, which are the width and heights of the 'sprite' from the texture. I've tried various other formulas, such as:
glTranslatef(x, y, 0);
The below three switching the negative sign to positive (x - y to x + y)
glTranslatef(sr->x/2 - sr->w/2, sr->y/2 - sr->h/2 0 );
glTranslatef(sr->x - sr->w/2, sr->y - sr->h/2, 0 );
glTranslatef(sr->x - sr->w, sr->y - sr->w, 0 );
glTranslatef(.5,.5,0);
It might also be helpful to say that:
glOrtho(0,screen_width,screen_height,0,-2,10);
is in use.
I've tried reading various tutorials, going through various forums, asking various people, but there doesn't seem to be a solution that works, nor can I find any useful resources that explain to me how I find the center of the image in order to translate it to '(0,0)'. I'm pretty new to OpenGL so a lot of this stuff takes awhile for me to digest.
Here's the entire function:
void Apply_Surface( float x, float y, Sheet_Container* source, Sheet_Rect* sr , float ang = 0, bool flipx = 0, bool flipy = 0, int e_x = -1, int e_y = -1 ) {
float imgwi,imghi;
glLoadIdentity();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D,source->rt());
// rotation
imghi = source->rh();
imgwi = source->rw();
Sheet_Rect t_shtrct(0,0,imgwi,imghi);
if ( sr == NULL ) // in case a sheet rect is not provided, assume it's width
//and height of texture with 0/0 x/y
sr = &t_shtrct;
glPushMatrix();
//
int wid, hei;
glGetTexLevelParameteriv(GL_TEXTURE_2D,0,GL_TEXTURE_WIDTH,&wid);
glGetTexLevelParameteriv(GL_TEXTURE_2D,0,GL_TEXTURE_HEIGHT,&hei);
glTranslatef(-sr->x + -sr->w,
-sr->y + -sr->h,0);
glRotatef(ang,0,0,1.f);
glTranslatef(sr->x + sr->w,
sr->y + sr->h,0);
// Yeah, out-dated way of drawing to the screen but it works for now.
GLfloat tex[] = {
(sr->x+sr->w * flipx) /imgwi, 1 - (sr->y+sr->h *!flipy )/imghi,
(sr->x+sr->w * flipx) /imgwi, 1 - (sr->y+sr->h * flipy)/imghi,
(sr->x+sr->w * !flipx) /imgwi, 1 - (sr->y+sr->h * flipy)/imghi,
(sr->x+sr->w * !flipx) /imgwi, 1 - (sr->y+sr->h *!flipy)/imghi
};
GLfloat vertices[] = { // vertices to put on screen
x, (y + sr->h),
x, y,
(x +sr->w), y,
(x +sr->w),(y +sr->h)
};
// index array
GLubyte index[6] = { 0,1,2, 2,3,0 };
float fx = (x/(float)screen_width)-(float)sr->w/2/(float)imgwi;
float fy = (y/(float)screen_height)-(float)sr->h/2/(float)imghi;
// activate arrays
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
// pass verteices and texture information
glVertexPointer(2, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, tex);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, index);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glPopMatrix();
glDisable(GL_TEXTURE_2D);
}
Sheet container class:
class Sheet_Container {
GLuint texture;
int width, height;
public:
Sheet_Container();
Sheet_Container(GLuint, int = -1,int = -1);
void Load(GLuint,int = -1,int = -1);
float rw();
float rh();
GLuint rt();
};
Sheet rect class:
struct Sheet_Rect {
float x, y, w, h;
Sheet_Rect();
Sheet_Rect(int xx,int yy,int ww,int hh);
};
Image loading function:
Sheet_Container Game_Info::Load_Image(const char* fil) {
ILuint t_id;
ilGenImages(1, &t_id);
ilBindImage(t_id);
ilLoadImage(const_cast<char*>(fil));
int width = ilGetInteger(IL_IMAGE_WIDTH), height = ilGetInteger(IL_IMAGE_HEIGHT);
return Sheet_Container(ilutGLLoadImage(const_cast<char*>(fil)),width,height);
}
Your quad (two triangles) is centered at:
( x + sr->w / 2, y + sr->h / 2 )
You need to move that point to the origin, rotate, and then move it back:
glTranslatef ( (x + sr->w / 2.0f), (y + sr->h / 2.0f), 0.0f); // 3rd
glRotatef (0,0,0,1.f); // 2nd
glTranslatef (-(x + sr->w / 2.0f), -(y + sr->h / 2.0f), 0.0f); // 1st
Here is where I think you are getting tripped up. People naturally assume that OpenGL applies transformations in the order they appear (top-to-bottom), that is not the case. OpenGL effectively swaps the operands everytime it multiplies two matrices:
M1 x M2 x M3
~~~~~~~
(1)
~~~~~~~~~~
(2)
(1) M2 * M1
(2) M3 * (M2 * M1) --> M3 * M2 * M1 (row-major / textbook math notation)
The technical term for this is post-multiplication, it all has to do with the way matrices are implemented in OpenGL (column-major). Suffice it to say, you should generally read glTranslatef, glRotatef, glScalef, etc. calls from bottom-to-top.
With that out of the way, your current rotation does not make any sense.
You are telling GL to rotate 0 degrees around an axis: <0,0,1> (the z-axis in other words). The axis is correct, but a 0 degree rotation is not going to do anything ;)