render_utility.py

from enum import Enum
from typing import Callable, List, Optional, Union

from OpenGL.constant import (Constant, FloatConstant, IntConstant,
                             LongConstant, StringConstant)
from OpenGL.GL import (GL_ALL_BARRIER_BITS, GL_BLEND, GL_COLOR_BUFFER_BIT,
                       GL_DEPTH_BUFFER_BIT, GL_DEPTH_TEST, GL_MAX, GL_MIN,
                       GL_ONE_MINUS_SRC_ALPHA, GL_SRC_ALPHA,
                       glBlendEquationSeparate, glBlendFunc, glClear,
                       glClearColor, glDisable, glDrawArrays,
                       glDrawArraysInstanced, glEnable, glLineWidth,
                       glMemoryBarrier, glPointSize)


def clear_screen(clear_color: List[float]) -> None:
    glClearColor(clear_color[0], clear_color[1],
                 clear_color[2], clear_color[3])
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)


class OGLRenderFunction(Enum):
    ARRAYS = 1
    ARRAYS_INSTANCED = 2


def generate_render_function(ogl_func: OGLRenderFunction,
                             primitive: Union[FloatConstant, IntConstant, LongConstant, StringConstant, Constant],
                             point_size: Optional[float] = None, line_width: Optional[float] = None, add_blending: bool = False,
                             depth_test: bool = False) -> Callable:

    def render_func(element_count: int) -> None:
        if add_blending:
            glEnable(GL_BLEND)
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
            glBlendEquationSeparate(GL_MIN, GL_MAX)
        else:
            glDisable(GL_BLEND)
        if depth_test:
            glEnable(GL_DEPTH_TEST)
        else:
            glDisable(GL_DEPTH_TEST)

        if point_size is not None:
            glPointSize(point_size)

        if line_width is not None:
            glLineWidth(line_width)

        if ogl_func is OGLRenderFunction.ARRAYS:
            glDrawArrays(primitive, 0, element_count)
        elif ogl_func is OGLRenderFunction.ARRAYS_INSTANCED:
            glDrawArraysInstanced(primitive, 0, 1, element_count)

        glMemoryBarrier(GL_ALL_BARRIER_BITS)

    return render_func