text: '''
      Renders a blue triangle
  '''
  
  import moderngl
  import numpy as np
  
  from window import Example, run_example
  
  
  class PerspectiveProjection(Example):
      gl_version = (3, 3)
      title = "Perspective Projection"
  
      def __init__(self, **kwargs):
          super().__init__(**kwargs)
  
          self.prog = self.ctx.program(
              vertex_shader='''
                  #version 330
  
                  in vec3 vert;
  
                  uniform float z_near;
                  uniform float z_far;
                  uniform float fovy;
                  uniform float ratio;
  
                  uniform vec3 center;
                  uniform vec3 eye;
                  uniform vec3 up;
  
                  mat4 perspective() {
                      float zmul = (-2.0 * z_near * z_far) / (z_far - z_near);
                      float ymul = 1.0 / tan(fovy * 3.14159265 / 360);
                      float xmul = ymul / ratio;
  
                      return mat4(
                          xmul, 0.0, 0.0, 0.0,
                          0.0, ymul, 0.0, 0.0,
                          0.0, 0.0, -1.0, -1.0,
                          0.0, 0.0, zmul, 0.0
                      );
                  }
  
                  mat4 lookat() {
                      vec3 forward = normalize(center - eye);
                      vec3 side = normalize(cross(forward, up));
                      vec3 upward = cross(side, forward);
  
                      return mat4(
                          side.x, upward.x, -forward.x, 0,
                          side.y, upward.y, -forward.y, 0,
                          side.z, upward.z, -forward.z, 0,
                          -dot(eye, side), -dot(eye, upward), dot(eye, forward), 1
                      );
                  }
  
                  void main() {
                      gl_Position = perspective() * lookat() * vec4(vert, 1.0);
                  }
              ''',
              fragment_shader='''
                  #version 330
  
                  out vec4 color;
  
                  void main() {
                      color = vec4(0.04, 0.04, 0.04, 1.0);
  
                  }
              ''',
          )
  
          self.prog['z_near'].value = 0.1
          self.prog['z_far'].value = 1000.0
          self.prog['ratio'].value = self.aspect_ratio
          self.prog['fovy'].value = 60
  
          self.prog['eye'].value = (3, 3, 3)
          self.prog['center'].value = (0, 0, 0)
          self.prog['up'].value = (0, 0, 1)
  
          grid = []
  
          for i in range(65):
              grid.append([i - 32, -32.0, 0.0, i - 32, 32.0, 0.0])
              grid.append([-32.0, i - 32, 0.0, 32.0, i - 32, 0.0])
  
          grid = np.array(grid)
  
          self.vbo = self.ctx.buffer(grid.astype('f4').tobytes())
          self.vao = self.ctx.simple_vertex_array(self.prog, self.vbo, 'vert')
  
      def render(self, time: float, frame_time: float):
          self.ctx.clear(1.0, 1.0, 1.0)
          self.vao.render(moderngl.LINES, 65 * 4)
  
  
  if __name__ == '__main__':
      run_example(PerspectiveProjection)
  