gles doesn't support glGetTexLevelParameter (though it anyway doesn't work on ANGLE)

texturewindow.cpp

@@ -52,6 +52,9 @@ void texture_window::threadfunc()
 	vao.bind();
 
 	while (!m_exit)
+	{
+		// if texture resized, update window size (maybe not necessary?)
+		if (GLAD_GL_VERSION_3_3 || GLAD_GL_ES_VERSION_3_1)
 		{
 			int w, h;
 			glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &w);
@@ -64,6 +67,7 @@ void texture_window::threadfunc()
 				m_win_h = h;
 				glfwSetWindowSize(m_window, w, h); // eh, not thread-safe (but works?)
 			}
+		}
 
 		glViewport(0, 0, m_win_w, m_win_h);