package opengl

// #cgo LDFLAGS: -framework OpenGL
//
// #include <OpenGL/gl.h>
import "C"
import (
	"image"
	"unsafe"
)

func Clp2(x uint64) uint64 {
	x -= 1
	x |= (x >> 1)
	x |= (x >> 2)
	x |= (x >> 4)
	x |= (x >> 8)
	x |= (x >> 16)
	x |= (x >> 32)
	return x + 1
}

type Texture struct {
	id            C.GLuint
	width         int
	height        int
	textureWidth  int
	textureHeight int
}

func createTexture(width, height int, pixels []uint8) *Texture {
	textureWidth := int(Clp2(uint64(width)))
	textureHeight := int(Clp2(uint64(height)))
	if pixels != nil {
		if width != textureWidth {
			panic("sorry, but width should be power of 2")
		}
		if height != textureHeight {
			panic("sorry, but height should be power of 2")
		}
	}
	texture := &Texture{
		id:            0,
		width:         width,
		height:        height,
		textureWidth:  textureWidth,
		textureHeight: textureHeight,
	}

	textureID := C.GLuint(0)
	C.glGenTextures(1, (*C.GLuint)(&textureID))
	if textureID == 0 {
		panic("glGenTexture failed")
	}
	C.glPixelStorei(C.GL_UNPACK_ALIGNMENT, 4)
	C.glBindTexture(C.GL_TEXTURE_2D, C.GLuint(textureID))

	ptr := unsafe.Pointer(nil)
	if pixels != nil {
		ptr = unsafe.Pointer(&pixels[0])
	}
	C.glTexImage2D(C.GL_TEXTURE_2D, 0, C.GL_RGBA,
		C.GLsizei(textureWidth), C.GLsizei(textureHeight),
		0, C.GL_RGBA, C.GL_UNSIGNED_BYTE, ptr)

	C.glTexParameteri(C.GL_TEXTURE_2D, C.GL_TEXTURE_MAG_FILTER, C.GL_LINEAR)
	C.glTexParameteri(C.GL_TEXTURE_2D, C.GL_TEXTURE_MIN_FILTER, C.GL_LINEAR)
	C.glBindTexture(C.GL_TEXTURE_2D, 0)

	// TODO: lock?
	texture.id = textureID

	return texture
}

func newTexture(width, height int) *Texture {
	return createTexture(width, height, nil)
}

func newTextureFromImage(img image.Image) *Texture {
	var pix []uint8
	switch img.(type) {
	case *image.RGBA:
		pix = img.(*image.RGBA).Pix
	case *image.NRGBA:
		pix = img.(*image.NRGBA).Pix
	default:
		panic("image should be RGBA or NRGBA")
	}
	size := img.Bounds().Size()
	return createTexture(size.X, size.Y, pix)
}