Mouse position on (OpenGL) scene

Question

I'm trying to get the mouse coordinate on OpenGL scene. My Code:

from PySide.QtGui import (QColor)
from PySide.QtCore import (Qt, QSize)
from PySide.QtOpenGL import (QGLWidget)
from OpenGL.GL import *
from OpenGL.GLU import *

class QGL(QGLWidget):
    def __init__(self, parent=None):
        self._pan_valid = False

        super(QGL, self).__init__(parent)
        self.setFocusPolicy(Qt.ClickFocus)

        self.local_translate = (0.0, 0.0, 0.0)
        self.zoomVal = 1.2

    def minimumSizeHint(self):
        return QSize(50, 50)

    def sizeHint(self):
        return QSize(800, 800)

    def initializeGL(self):
        self.qglClearColor(QColor.fromCmykF(0.0, 0.1, 0.0, 0.882))
        glViewport( 0, 0, self.width(), self.height())
        glEnable(GL_TEXTURE_2D)
        glEnable(GL_CULL_FACE)
        glEnable(GL_MULTISAMPLE)
        glEnable(GL_LINE_SMOOTH, GL_LINE_WIDTH, GL_ALIASED_LINE_WIDTH_RANGE)
        glShadeModel(GL_FLAT)
        glEnable(GL_DEPTH_TEST)
        glHint(GL_LINE_SMOOTH_HINT,  GL_NICEST)
        glDepthRange (0.1, 1.0)

    def paintGL(self):
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
        gluOrtho2D(-self.zoomVal, +self.zoomVal, -self.zoomVal, +self.zoomVal)
        glLoadIdentity()

        genList = glGenLists(1)
        glNewList(genList, GL_COMPILE)

        vertices = [
            (0,0,0),
            (0.5,0,0),
            (0.5,0.5,0),
            (0,0.5,0)
        ]

        glBegin(GL_QUADS)
        self.qglColor(QColor(0,255,255))
        for vertex in vertices:
            glVertex3fv(vertex)
        glEnd()

        glEndList()
        glCallList(genList)

    def mousePressEvent(self, event):
        print event.pos()
        print self.mapToGlobal(event.pos())

when I do this:

print event.pos()

it will give me the mouse position on the window.

and when I do this:

print self.mapToGlobal(event.pos())

it will give me the mouse position on the monitor.

How can I get the mouse position on the scene? I'm using 2D viewport (gluOrtho2D).

score 1 · Accepted Answer · answered Apr 21 '18 at 18:07

I don't think there is a convenient built-in function for this, but it should be trivial to calculate, especially given that this is a 2D, orthographic scene. You know the size of the window in pixels, and you know where in that window the user clicked, given whatever event.pos() returns (also in pixels). What needs to happen then is that you need to map that range in pixels to your range specified in your gluOrtho2D call. The following code could be adapted as you see fit:

#specifying a bunch of example values
zoom_val = 1.2
window_size = (800, 600)
mouse_pos = (300, 150)
ortho_2d = (-zoom_val, +zoom_val, -zoom_val, +zoom_val)

#First, calculate the "normalized" mouse coordinates by dividing by window_size
mouse_norm_x = mouse_pos[0] / window_size[0]
mouse_norm_y = mouse_pos[1] / window_size[1]

#Now map those coordinates to your orthographic projection range
mouse_ortho_x = (mouse_norm_x * (ortho_2d[1] - ortho_2d[0])) + ortho_2d[0]
mouse_ortho_y = (mouse_norm_y * (ortho_2d[3] - ortho_2d[2])) + ortho_2d[2]
mouse_ortho = (mouse_ortho_x, mouse_ortho_y)
print(mouse_ortho)

Getting the z-coordinate is trickier. I would suggest reading up on the concept of "mouse-picking" for that. You would need to get the depth buffer, store its results in a texture, and sample the mouse coordinate at the appropriate location in that texture to get the z-coordinate. You can combine these two answers (1, 2) I have previously written for other questions together to get something working. Let me know if this helps!

I see... yeah, that works perfectly, just that when dividing `mouse_pos[0] / window_size[0]` I changed it to `float(mouse_pos[0]) / float(self.width())` and `float(mouse_pos[1]) / float(self.height())`. — Bear, Apr 23 '18 at 08:19
also, yeah, I saw an article about `Mouse Picking with Ray Casting`, but I don't need 3 dimensions yet, probably I'll consider it sometimes in future. — Bear, Apr 23 '18 at 08:25

Mouse position on (OpenGL) scene

1 Answers1