I'm trying to detect if my mouse is hovering over a rectangle that I drew(with VBOs), but when I get the mouse coordinates with Mouse.getX() & Mouse.getY(), it returns the window coordinates(i.e. (480, 200)). How can I get the mouse coordinates from the range of [-1, 1]?
trivial approach
You can do this by knowing only the viewport or if drawing in the whole window its inner size. Assuming mouse coordinates are 0,0 in the top left corner.
The following will normalize the input to [-1, 1].
double normalizedX = -1.0 + 2.0 * (double)Mouse.getX() / window.width;
double normalizedY = 1.0 - 2.0 * (double)Mouse.getY() / window.height;
You can also use a more intricate solution by creating an inverse matrix for the viewport and multiply out the mouse input vector.
Related
I want rotate a QGraphicsPixmapItem around a point according to mouse position.
So i tried this:
void Game::mouseMoveEvent(QMouseEvent* e){
setMouseTracking(true);
QPoint midPos((sceneRect().width() / 2), 0), currPos;
currPos = QPoint(mapToScene(e->pos()).x(), mapToScene(e->pos()).y());
QPoint itemPos((midPos.x() - cannon->scenePos().x()), (midPos.y() - cannon->scenePos().y()));
double angle = atan2(currPos.y(), midPos.x()) - atan2(midPos.y(), currPos.x());
cannon->setTransformOriginPoint(itemPos);
cannon->setRotation(angle); }
But the pixmap moves a few of pixels.
I want a result like this:
Besides the mixup of degrees and radians that #rafix07 pointed out there is a bug in the angle calculation. You basically need the angle of the line from midPos to currPos which you calculate by
double angle = atan2(currPos.y() - midPos.y(), currPos.x() - midPos.x());
Additionally the calculation of the transformation origin assumes the wrong coordinate system. The origin must be given in the coordinate system of the item in question (see QGraphicsItem::setTransformOriginPoint), not in scene coordinates. Since you want to rotate around the center of that item it would just be:
QPointF itemPos(cannon->boundingRect().center());
Then there is the question whether midPos is actually the point highlighted in your image in the middle of the canon. The y-coordinate is set to 0 which would normally be the edge of the screen, but your coordinate system may be different.
I would assume the itemPos calculated above is just the right point, you only need to map it to scene coordinates (cannon->mapToScene(itemPos)).
Lastly I would strongly advise against rounding scene coordinates (which are doubles) to ints as it is done in the code by forcing it to QPoints instead of QPointFs. Just use QPointF whenever you are dealing with scene coordinates.
I have built a small custom qml item that is used as a selection area (something like the QRubberBand component provided in Qt Widgets). The item also give the ability to user to resize the content of the selection, so by grabbing the bottom corner of the selection rectangle it is possible to drag to enlarge the content. After the user has done resizing I would like to compute the QTransform matrix of the transformation. QTransform provides a convenient QTransform::scale method to get a scale transformation matrix (which I can use by comparing the width and height ratio with the previous size of the selection). The problem is that QTransform::scale assumes that the center point of the transformation is the center of the object, but I would like my transformation origin to be the top left of the selection (since the user is dragging from the bottom-right).
So for example, if I have the following code:
QRectF selectionRect = QRectF(QPointF(10,10), QPointF(200,100));
// let's resize the rectangle by changing its bottom-right corner
auto newSelectionRect = selectionRect;
newSelectionRect.setBottomRight(QPointF(250, 120));
QTransform t;
t.scale(newSelectionRect.width()/selectionRect.width(), newSelectionRect.height()/selectionRect.height());
The problem here is that if I apply the transformation t to my original selectionRect I don't get my new rectangle newSelectionRect back, but I get the following:
QRectF selectionRect = QRectF(QPointF(10,10)*sx, QPointF(200,100)*sy);
where sx and sy are the scale factors of the transform. I would like a way to compute the QTransform of my transformation that gives back newSelectionRect when applied to selectionRect.
The problem lies in this assumption:
QTransform::scale assumes that the center point of the transformation is the center of the object
All transformations performed by QTransform are referred to the origin of the axis, is just an application of various tranformation matrixes (https://en.wikipedia.org/wiki/Transformation_matrix):
Also, QTransform::translate (https://doc.qt.io/qt-5/qtransform.html#translate) states:
Moves the coordinate system dx along the x axis and dy along the y axis, and returns a reference to the matrix.
Thereby, what you are looking for is:
QTransform t;
t.translate(+10, +10); // Move the origin to the top left corner of the rectangle
t.scale(newSelectionRect.width()/selectionRect.width(), newSelectionRect.height()/selectionRect.height()); // scale
t.translate(-10, -10); // move the origin back to where it was
QRectF resultRect = t.mapRect(selectionRect); // resultRect == newSelectionRect!
I am making a 2D board game. the game board grid is 8x8 and each cell of the grid is an object. So a board consists of 64 cell objects. My aim is to work out which cell the mouse is in. I am attempting this by tracking the mouse coordinates and comparing it to the grid coordinates.
my coordinate system is as follows:
gluOrtho2D(-4,4,-4,4);
I am trying to get the current mouse position by using the following in my update function:
POINT p
if (GetCursorPos(&p)){
}
if (ScreenToClient(hWnd, &p))
{
}
However although this is tracking the coordinates of the mouse it is not correctly tracking the world coordinates that I set with gluOrtho2D. How can I achieve this?
It depends on your glViewPort
Let's say you have:
glViewport(0,0, 640, 640);
The mouse position is (mousePos.x,mousePos.y) and the world position you want to know is (world.x, world.y)
And, give that the top/left corner of your screen is the (0, 0) coordinate
Then we can make the following:
world.x = -4.0 + (mousePos.x / 640.0) * (4*2)
world.y = 4.0 - (mousePos.y / 640.0) * (4*2)
What we are doing here is a linear interpolation using the normalize position of the mouse within the screen (mousePos.x / 640) and then multiplying this value to the width of the word (4*2).
Given that the top/left corner of the grid start at (-4, 4), we add the offset of the world position.
I have managed to rotate a rectangle in OpenGL (C++) just fine. I am making a program that tests two rectangles for collision using the "separated axis theorem". To use the theorem, I need the x and y coordinates of each corner of the rectangle, but my problem is that, although I call glRotatef(...), the coordinates of the corners of the rectangle are not changed to the values that they are rotated too, but the rectangle rotates as it should. How can I update the coordinates of my rectangle after glRotatef is called?
Code:
// float r1.x[4] and r1.y[4] hold the x and y position of each of the 4 corners, starting with the upper left (r1.x[0], r1.y[0])
glLoadIdentity();
glTranslatef((r1.x[0] + r1.x[2]) / 2, (r1.y[1] + r1.y[3]) / 2, 0); // Translates matrix to center of rectangle
glRotatef(r1.angle, 0, 0, 1);
glTranslatef(-((r1.x[0] + r1.x[2]) / 2), -((r1.y[1] + r1.y[3]) / 2), 0); // Translates back
r1.angle++;
glBegin(GL_QUADS);
glVertex2f(r1.x[0], r1.y[0]);
glVertex2f(r1.x[1], r1.y[1]);
glVertex2f(r1.x[2], r1.y[2]);
glVertex2f(r1.x[3], r1.y[3]);
glEnd();
Transformation calls in OpenGL (like glTranslatef and glRotatef) update an internal transformation matrix that get multiplied by the points you provide before getting drawn on the screen. OpenGL does not at all touch your data.
In general, that is what you want. You have a model that is constant in time, but it gets transformed around.
If however, you do need to update your data, you need to create your own transformation matrix, manually multiply it and then draw with a clean transformation matrix (with glLoadIdentity)
You could get a little help from OpenGL though, as you can get the transformation matrix from OpenGL, but I don't recommend this. The math is not that hard and you'd appreciate learning how to do it.
I'm currently calling Trace (method below) from a game loop. Right now all I'm trying to do is get the world coordinates from the screen mouse so I can move objects around in the world space. The values I'm getting from gluUnProject are however; puzzling me.
I was using glReadPixel(...) to get the Z value but that produced little to no movement in the object I was drawing and the resulting vector ended up being the same as my cameras location (except for the tiny decimal changes due to mouse movement), so I decided to get rid of the call and replace the Z value with 1.
My question is: Does the following code look right to you? Every example I've seen thusfar is either identical or -very- similar but I can't seem to produce correct results, even if I lock down the Y axis. If the code is correct, then I'm guessing that I'm just not using the resulting vector properly. Should I not be able to draw an object or point directly with the resulting vector or do I have to do something else with it, like normalize?
The current render mode is GL_RENDER and I am using glFrustum with a NearZ value of 1 and FarZ value of 2048, to create a perspective. There is also a series of viewports created along with scissors, with a size and width of 512x768 and positioned in each corner of a 1024x768 window. Trace(...) is called in between rendering of the upper left viewport and is the only perspective projection, while the other viewports are orthographic. FOV is set to 45.
void VideoWindow::Trace(int cursorX, int cursorY)
{
double objX, objY, objZ;//holder for world coordinates
GLint view[4];//viewport dimensions+pos
GLdouble p[16];//projection matrix
GLdouble m[16];//modelview matrix
GLdouble z;//Z-Buffer Value?
glGetDoublev (GL_MODELVIEW_MATRIX, m);
glGetDoublev (GL_PROJECTION_MATRIX,p);
glGetIntegerv( GL_VIEWPORT, view );
//view[3]-cursorY = conversion from upper left (0,0) to lower left (0,0)
//Unproject 2D Screen coordinates into wonderful world coordinates
gluUnProject(cursorX, view[3]-cursorY, 1, m, p, view, &objX, &objY, &objZ);
//Do something useful here???
}
Any ideas?
Edit: I've changed the winZ value to 0.5 instead of 1 which gives a vector thats more reasonable but drawing a point still wasn't matching the mouse. I found out that the value of view[3] was 384 which is correct for the viewport I'm using but I replaced it with 768 (the actual window size) and the point followed the mouse 100%. Further experimentation reveals that I can't use the coordinates to move around a 3D object in the perspective world space using this these coordinates however moving around 3D object in Orthographic space works fine.
The winz argument to gluUnproject specifies the depth from the camera at which you're "picking" your points. As you've stated this coordinate should be in the [0, 1] range.
Some tutorials like NeHes read out the z coordinate from the depth buffer so that you "pick" at the right depth, of course for this to work you'll have to do the gluUnproject after you've rendered everything else.
Regardless, if you set winz to 0.5 or something (not 0 or 1 or the point will end up on the near or far clip plane, and maybe culled) and do the following:
gluUnProject(cursorX, view[3]-cursorY, 0.5, m, p, view, &objX, &objY, &objZ);
//Do something useful here???
glPointSize(10);
glBegin(GL_POINTS);
glColor3f(1, 0, 0);
glVertex3f(objX, objY, objZ);
glEnd();
You should end up with a red blob at the mouse pointer (provided nothing else overdraws it afterwards and you don't have any funny render states which renders the point invisible).
just a thought, but if the third argument to gluUnProject is the z distance to the camera, wouldn't any point you draw at that location be on the near clipping plane of your frustum?
Better make that z value a bit higher.