import ctypes
import OpenGL.GL as gl
from sdl2 import * #everything has a SDL_ prefix. ick!
import numpy as np

W,H=640,480
FPS=60
frame_minticks=1000/60

# === SDL/OpenGL init ===

SDL_Init(SDL_INIT_VIDEO)

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION,3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION,3);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE,24);

window=SDL_CreateWindow("OpenGL test",100,100,W,H,SDL_WINDOW_OPENGL|SDL_WINDOW_SHOWN)

context=SDL_GL_CreateContext(window)
SDL_GL_SetSwapInterval(0)

gl.glClearColor(1.0,1.0,1.0,1.0)
gl.glClear(gl.GL_COLOR_BUFFER_BIT|gl.GL_DEPTH_BUFFER_BIT)    
SDL_GL_SwapWindow(window)

# === shader compilation ===

shader_program=gl.glCreateProgram()
shader_vertex=gl.glCreateShader(gl.GL_VERTEX_SHADER)
shader_fragment=gl.glCreateShader(gl.GL_FRAGMENT_SHADER)

gl.glShaderSource(shader_vertex,    """
                                    #version 330
                                    attribute vec3 position;
                                    attribute vec4 color;
                                    varying vec4 v_color;
                                    void main()
                                        {
                                        gl_Position=vec4(position,1.0);
                                        v_color=color;
                                        }
                                    """)
gl.glShaderSource(shader_fragment,  """
                                    #version 330
                                    varying vec4 v_color;
                                    void main()
                                        {
                                        gl_FragColor=v_color;
                                        }
                                    """)

gl.glCompileShader(shader_vertex)
print "=== vertex shader log ==="
if gl.glGetShaderiv(shader_vertex,gl.GL_COMPILE_STATUS):
    print "OK"
else:
    log=gl.glGetShaderInfoLog(shader_vertex)
    print log

gl.glCompileShader(shader_fragment)
print "=== fragment shader log ==="
if gl.glGetShaderiv(shader_fragment,gl.GL_COMPILE_STATUS):
    print "OK"
else:
    log=gl.glGetShaderInfoLog(shader_fragment)
    print log

print "=== end shader logs ==="

gl.glAttachShader(shader_program,shader_vertex)
gl.glAttachShader(shader_program,shader_fragment)
gl.glLinkProgram(shader_program)

gl.glUseProgram(shader_program)

# === buffer creation ===

vertex_data=np.zeros(4,dtype=[("position",np.float32,3),("color",np.float32,4)])
vertex_data[1]=((-1,-1,1),(1,0,0,1))
vertex_data[0]=(( 1,-1,1),(0,1,0,1))
vertex_data[2]=(( 1, 1,1),(0,0,1,1))
vertex_data[3]=((-1, 1,1),(1,1,0,1))

vertex_buffer=gl.glGenBuffers(1)
gl.glBindBuffer(gl.GL_ARRAY_BUFFER,vertex_buffer)
gl.glBufferData(gl.GL_ARRAY_BUFFER,vertex_data.nbytes,vertex_data,gl.GL_DYNAMIC_DRAW)

# === buffer binding ===

stride=vertex_data.strides[0]

offset=ctypes.c_void_p(0)
loc=gl.glGetAttribLocation(shader_program,"position")
gl.glEnableVertexAttribArray(loc)
gl.glBindBuffer(gl.GL_ARRAY_BUFFER,vertex_buffer)
gl.glVertexAttribPointer(loc,3,gl.GL_FLOAT,False,stride,offset)

offset=ctypes.c_void_p(vertex_data.dtype["position"].itemsize)
loc=gl.glGetAttribLocation(shader_program,"color")
gl.glEnableVertexAttribArray(loc)
gl.glBindBuffer(gl.GL_ARRAY_BUFFER,vertex_buffer)
gl.glVertexAttribPointer(loc,4,gl.GL_FLOAT,False,stride,offset)

# === main loop ===

event=SDL_Event()
while True:
    frame_startticks=SDL_GetTicks()
    
    while SDL_PollEvent(ctypes.byref(event))!=0:
        if event.type==SDL_QUIT:
            SDL_DestroyWindow(window)
            SDL_Quit()
            raise SystemExit("clean exit")
    
    gl.glClear(gl.GL_COLOR_BUFFER_BIT|gl.GL_DEPTH_BUFFER_BIT)
    
    gl.glDrawArrays(gl.GL_TRIANGLE_STRIP, 0, 4)
    
    SDL_GL_SwapWindow(window)
    
    frame_endticks=SDL_GetTicks()
    frame_spentticks=frame_endticks-frame_startticks
    if(frame_spentticks<frame_minticks):
        SDL_Delay(frame_minticks-frame_spentticks)