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  • ### BEGIN GPL LICENSE BLOCK #####
    #
    #  This program is free software; you can redistribute it and/or
    #  modify it under the terms of the GNU General Public License
    #  as published by the Free Software Foundation; either version 2
    #  of the License, or (at your option) any later version.
    #
    #  This program is distributed in the hope that it will be useful,
    #  but WITHOUT ANY WARRANTY; without even the implied warranty of
    #  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    #  GNU General Public License for more details.
    #
    #  You should have received a copy of the GNU General Public License
    #  along with this program; if not, write to the Free Software Foundation,
    #  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
    #
    # ##### END GPL LICENSE BLOCK #####
    
    
    import gpu
    from gpu_extras.batch import batch_for_shader
    from mathutils import Vector
    
    
    
    if bpy.app.background:  # ignore north line in background mode
        def north_update(self, context):
            pass
    else:
        vertex_shader = '''
            uniform mat4 u_ViewProjectionMatrix;
    
            in vec3 position;
    
            flat out vec2 v_StartPos;
            out vec4 v_VertPos;
    
            void main()
            {
                vec4 pos    = u_ViewProjectionMatrix * vec4(position, 1.0f);
                gl_Position = pos;
                v_StartPos    = (pos / pos.w).xy;
                v_VertPos     = pos;
            }
        '''
    
        fragment_shader = '''
            uniform vec4 u_Color;
    
            flat in vec2 v_StartPos;
            in vec4 v_VertPos;
    
            uniform vec2 u_Resolution;
    
            void main()
            {
                vec4 vertPos_2d = v_VertPos / v_VertPos.w;
                vec2 dir  = (vertPos_2d.xy - v_StartPos.xy) * u_Resolution;
                float dist = length(dir);
    
                if (step(sin(dist / 5.0f), 0.0) == 1) discard;
    
                gl_FragColor = u_Color;
            }
        '''
    
        shader = gpu.types.GPUShader(vertex_shader, fragment_shader)
    
        def draw_north_callback():
            # ------------------------------------------------------------------
            # Set up the compass needle using the current north offset angle
            # less 90 degrees.  This forces the unit circle to begin at the
            # 12 O'clock instead of 3 O'clock position.
            # ------------------------------------------------------------------
            sun_props = bpy.context.scene.sun_pos_properties
    
            color = (0.2, 0.6, 1.0, 0.7)
            radius = 100
            angle = -(sun_props.north_offset - math.pi / 2)
            x = math.cos(angle) * radius
            y = math.sin(angle) * radius
    
            coords = Vector((x, y, 0)), Vector((0, 0, 0))   # Start & end of needle
    
            batch = batch_for_shader(
                shader, 'LINE_STRIP',
                {"position": coords},
            )
            shader.bind()
    
            matrix = bpy.context.region_data.perspective_matrix
            shader.uniform_float("u_ViewProjectionMatrix", matrix)
            shader.uniform_float("u_Resolution", (bpy.context.region.width, bpy.context.region.height))
            shader.uniform_float("u_Color", color)
            bgl.glLineWidth(2.0)
            batch.draw(shader)
    
    
        _handle = None
    
    
        def north_update(self, context):
            global _handle
            if self.show_north and _handle is None:
                _handle = bpy.types.SpaceView3D.draw_handler_add(draw_north_callback, (), 'WINDOW', 'POST_VIEW')
            elif _handle is not None:
                bpy.types.SpaceView3D.draw_handler_remove(_handle, 'WINDOW')
                _handle = None
            context.area.tag_redraw()