Draw points on screen with bgl? (python)

Question

I'd like to use bgl to draw dots points on 2d screen from 3d vertices in scene. I have lines working by using bgl.GL_LINE_LOOP but I couldn't find the full list of bgl.GL_* to loop up for points.

Answer 1

short answer:

bgl.glPointSize(5) bgl.glBegin(bgl.GL_POINTS)

less shorter answer:

Open template operator_modal_draw.py

In draw_callback_px(self, context) I call my function

DrawByVertices("points", verts2d, [0.5, 1, 0.1, 0.5])

where verts2d are screen coordinates [(screen.x, screen.y), ..] in my case derived from vector3 like this

from bpy_extras.view3d_utils import location_3d_to_region_2d
#...
verts2d = []
for v in bm.verts:
    new2dCo = location_3d_to_region_2d(context.region, \
                                       context.space_data.region_3d, \
                                       v.co)
    verts2d.append([new2dCo.x,new2dCo.y])

.

def DrawByVertices(mode, verts2d, color):
    bgl.glColor4f(*color)
    bgl.glEnable(bgl.GL_BLEND)

    if mode is "points":
        bgl.glPointSize(5)
        bgl.glBegin(bgl.GL_POINTS)    
    elif mode is "lines":
        bgl.glLineWidth(2)
        bgl.glBegin(bgl.GL_LINE_LOOP)

    for x, y in verts2d:
        bgl.glVertex2f(x, y)

    bgl.glEnd()
    bgl.glDisable(bgl.GL_BLEND)
    #restore defaults
    bgl.glLineWidth(1)
    bgl.glColor4f(0.0, 0.0, 0.0, 1.0)

    return

Result is colored points drawn on screen over 3d vertex coordinates.

Answer 2

You can use OpenGL's feature for stippled lines to draw dotted / dashed lines:

import bpy
import bgl
import blf


def draw_callback_px(self, context):

    bgl.glPushAttrib(bgl.GL_ENABLE_BIT)
    # glPushAttrib is done to return everything to normal after drawing

    bgl.glLineStipple(1, 0x9999)
    bgl.glEnable(bgl.GL_LINE_STIPPLE)

    font_id = 0  # XXX, need to find out how best to get this.

    # draw some text
    blf.position(font_id, 15, 30, 0)
    blf.size(font_id, 20, 72)
    blf.draw(font_id, "Hello Word " + str(len(self.mouse_path)))

    # 50% alpha, 2 pixel width line
    bgl.glEnable(bgl.GL_BLEND)
    bgl.glColor4f(0.0, 0.0, 0.0, 0.5)
    bgl.glLineWidth(2)

    bgl.glBegin(bgl.GL_LINE_STRIP)
    for x, y in self.mouse_path:
        bgl.glVertex2i(x, y)

    bgl.glEnd()
    bgl.glPopAttrib()

    # restore opengl defaults
    bgl.glLineWidth(1)
    bgl.glDisable(bgl.GL_BLEND)
    bgl.glColor4f(0.0, 0.0, 0.0, 1.0)


class ModalDrawOperator(bpy.types.Operator):
    """Draw a line with the mouse"""
    bl_idname = "view3d.modal_operator"
    bl_label = "Simple Modal View3D Operator"

    def modal(self, context, event):
        context.area.tag_redraw()

        if event.type == 'MOUSEMOVE':
            self.mouse_path.append((event.mouse_region_x, event.mouse_region_y))

        elif event.type == 'LEFTMOUSE':
            bpy.types.SpaceView3D.draw_handler_remove(self._handle, 'WINDOW')
            return {'FINISHED'}

        elif event.type in {'RIGHTMOUSE', 'ESC'}:
            bpy.types.SpaceView3D.draw_handler_remove(self._handle, 'WINDOW')
            return {'CANCELLED'}

        return {'RUNNING_MODAL'}

    def invoke(self, context, event):
        if context.area.type == 'VIEW_3D':
            # the arguments we pass the the callback
            args = (self, context)
            # Add the region OpenGL drawing callback
            # draw in view space with 'POST_VIEW' and 'PRE_VIEW'
            self._handle = bpy.types.SpaceView3D.draw_handler_add(draw_callback_px, args, 'WINDOW', 'POST_PIXEL')

            self.mouse_path = []

            context.window_manager.modal_handler_add(self)
            return {'RUNNING_MODAL'}
        else:
            self.report({'WARNING'}, "View3D not found, cannot run operator")
            return {'CANCELLED'}


def register():
    bpy.utils.register_class(ModalDrawOperator)


def unregister():
    bpy.utils.unregister_class(ModalDrawOperator)

if __name__ == "__main__":
    register()

If you want to draw circles in arbitrary size, you'll have to roll your own primitive drawing function for ellipses / circles (basically a regular polygon with as many edges as required to make it look round).