glBufferSubData not working, doesn't show error

Question

I'm making a basic voxel rendering class with python using glfw. I'm using glBufferSubData instead of glBufferData, but it won't render. Here is the code that is suspected to be causing the problem:

# imports
import glfw, numpy as np
from OpenGL.GL import *
from ctypes import *
from core.texture_manager import *

glfw.init()

class VBOManager:
    def __init__(self, renderer):
        self.renderer = renderer
        self.run()
    
    def run(self):
        for i in self.renderer.to_add[:self.renderer.to_add_count]:
            self.renderer.vertices.extend(i[0])
            self.renderer.texCoords.extend(i[1])
            vertices = np.array(i[0], dtype=np.float32)
            texCoords = np.array(i[1], dtype=np.float32)

            # use glBufferSubData
            glBindBuffer(GL_ARRAY_BUFFER, self.renderer.vbo)
            glBufferData(GL_ARRAY_BUFFER, self.renderer.vertices.nbytes, vertices.nbytes, (c_float * len(vertices))(*vertices))
            glFlush()
            glVertexPointer(3, GL_FLOAT, 0, None)
            glTexCoordPointer(3, GL_FLOAT, 0, None)
            glBindBuffer(GL_ARRAY_BUFFER, self.renderer.vbo_1)
            glBufferSubData(GL_ARRAY_BUFFER, self.renderer.texCoords.nbytes, texCoords.nbytes, (c_float * len(texCoords))(*texCoords))
            glFlush()

            self.renderer.to_add.remove(i)

class TerrainRenderer:
    def __init__(self, window):
        self.window = window

        self.vertices = np.array([])
        self.texCoords = np.array([])

        self.to_add = []
        self.to_add_count = 256

        self.vbo, self.vbo_1 = glGenBuffers (2)
        glBindBuffer(GL_ARRAY_BUFFER, self.vbo)
        glBufferData(GL_ARRAY_BUFFER, 12 * 4, None, GL_STATIC_DRAW)
        self.vbo_manager = VBOManager(self)

        self.texture_manager = TextureAtlas()

        glEnable(GL_TEXTURE_2D)
        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
        glEnableClientState(GL_TEXTURE_COORD_ARRAY)
        glEnableClientState (GL_VERTEX_ARRAY)

    def render(self):
        try:
            self.vbo_manager.run()
        except RuntimeError:
            pass

        glClear (GL_COLOR_BUFFER_BIT)

        glEnable(GL_TEXTURE_2D)
        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
        glBindBuffer (GL_ARRAY_BUFFER, self.vbo)
        glVertexPointer (3, GL_FLOAT, 0, None)
        glBindBuffer(GL_ARRAY_BUFFER, self.vbo_1)
        glTexCoordPointer(2, GL_FLOAT, 0, None)

        glDrawArrays (GL_QUADS, 0, len(self.vertices))
        glDisable(GL_TEXTURE_2D)
        glDisable(GL_BLEND)

    def add(self, posList, texCoords):
        self.to_add.append((numpy.array(posList), numpy.array(texCoords)))

When I start the application that uses this code, it shows no logs, warnings or errors, but it also doesn't render the vertices at all. NOTHING is visible on the screen.

Answer 1

glBufferSubData just updates a buffer object's data store but doesn't creates a buffer object's data store. You need to create the buffer object's data store with glBufferData, after that you can update the data with glBufferSubData. Furthermore, The 2nd argument of glBufferSubData specifies the offset into the buffer object's data store where data replacement will begin.

glBindBuffer(GL_ARRAY_BUFFER, self.vbo_1)
glBufferData(GL_ARRAY_BUFFER, texCoords.nbytes, None, GL_STATIC_DRAW)

glBindBuffer(GL_ARRAY_BUFFER, self.renderer.vbo_1)
glBufferSubData(GL_ARRAY_BUFFER, 0, texCoords.nbytes, (c_float * len(texCoords))(*texCoords))