package opengl

// #cgo LDFLAGS: -framework OpenGL
//
// #include <OpenGL/gl.h>
import "C"
import (
	"fmt"
	"github.com/hajimehoshi/go-ebiten/graphics"
)

type RenderTarget struct {
	framebuffer C.GLuint
	width       int
	height      int
	flipY       bool
}

func createFramebuffer(nativeTexture C.GLuint) C.GLuint {
	framebuffer := C.GLuint(0)
	C.glGenFramebuffers(1, &framebuffer)

	C.glBindFramebuffer(C.GL_FRAMEBUFFER, framebuffer)

	C.glFramebufferTexture2D(C.GL_FRAMEBUFFER, C.GL_COLOR_ATTACHMENT0,
		C.GL_TEXTURE_2D, nativeTexture, 0)
	if C.glCheckFramebufferStatus(C.GL_FRAMEBUFFER) !=
		C.GL_FRAMEBUFFER_COMPLETE {
		panic("creating framebuffer failed")
	}

	// Set this framebuffer opaque because alpha values on a target might be
	// confusing.
	C.glClearColor(0, 0, 0, 1)
	C.glClear(C.GL_COLOR_BUFFER_BIT)

	return framebuffer
}

func (r *RenderTarget) setAsViewport() {
	C.glFlush()

	C.glBindFramebuffer(C.GL_FRAMEBUFFER, C.GLuint(r.framebuffer))
	err := C.glCheckFramebufferStatus(C.GL_FRAMEBUFFER)
	if err != C.GL_FRAMEBUFFER_COMPLETE {
		panic(fmt.Sprintf("glBindFramebuffer failed: %d", err))
	}

	C.glBlendFuncSeparate(C.GL_SRC_ALPHA, C.GL_ONE_MINUS_SRC_ALPHA,
		C.GL_ZERO, C.GL_ONE)

	width := graphics.AdjustSizeForTexture(r.width)
	height := graphics.AdjustSizeForTexture(r.height)
	C.glViewport(0, 0, C.GLsizei(width), C.GLsizei(height))
}

func (r *RenderTarget) projectionMatrix() [4][4]float64 {
	width := graphics.AdjustSizeForTexture(r.width)
	height := graphics.AdjustSizeForTexture(r.height)
	matrix := graphics.OrthoProjectionMatrix(0, width, 0, height)
	if r.flipY {
		matrix[1][1] *= -1
		matrix[1][3] += float64(r.height) /
			float64(graphics.AdjustSizeForTexture(r.height)) * 2
	}
	return matrix
}

func (r *RenderTarget) dispose() {
	C.glDeleteFramebuffers(1, &r.framebuffer)
}