package render

import (
	"unsafe"

	"github.com/go-gl/gl/all-core/gl"
)

var (
	screenQuadVerts = []float32{
		-1, -1,
		0, 0,
		1, -1,
		1, 0,
		1, 1,
		1, 1,
		-1, -1,
		0, 0,
		1, 1,
		1, 1,
		-1, 1,
		0, 1,
	}
	screenQuadVAO uint32
	screenQuadVBO uint32
)

func initScreenQuad() {
	gl.GenBuffers(1, &screenQuadVBO)
	gl.BindBuffer(gl.ARRAY_BUFFER, screenQuadVBO)
	gl.BufferData(gl.ARRAY_BUFFER, int(unsafe.Sizeof(float32(0)))*len(screenQuadVerts), gl.Ptr(screenQuadVerts), gl.STATIC_DRAW)

	gl.GenVertexArrays(1, &screenQuadVAO)
	gl.BindVertexArray(screenQuadVAO)

	gl.VertexAttribPointer(0, 2, gl.FLOAT, false, int32(4*unsafe.Sizeof(float32(0))), gl.PtrOffset(0))
	gl.VertexAttribPointer(1, 2, gl.FLOAT, false, int32(4*unsafe.Sizeof(float32(0))), gl.PtrOffset(int(2*unsafe.Sizeof(float32(0)))))
	gl.EnableVertexAttribArray(0)
	gl.EnableVertexAttribArray(1)
}

// drawScreenQuad draws a Quad covering the entire screen.
//
// Attribute: vert:     [ -1.0 --> 1.0]
func (r *WorldRenderer) drawScreenQuad() {
	if screenQuadVAO == 0 {
		initScreenQuad()
	}

	gl.Disable(gl.DEPTH_TEST)
	gl.Disable(gl.CULL_FACE)
	gl.BindVertexArray(screenQuadVAO)
	gl.DrawArrays(gl.TRIANGLES, 0, 6)
}