ebiten/graphics/opengl/rendertarget/render_target.go

package rendertarget

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

type NativeTexture C.GLuint

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

func NewWithCurrentFramebuffer(width, height int) *RenderTarget {
	framebuffer := C.GLint(0)
	C.glGetIntegerv(C.GL_FRAMEBUFFER_BINDING, &framebuffer)
	rt := &RenderTarget{C.GLuint(framebuffer), width, height, true}
	rt.setAsViewport()
	return rt
}

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

	origFramebuffer := C.GLint(0)
	C.glGetIntegerv(C.GL_FRAMEBUFFER_BINDING, &origFramebuffer)

	C.glBindFramebuffer(C.GL_FRAMEBUFFER, framebuffer)
	defer C.glBindFramebuffer(C.GL_FRAMEBUFFER, C.GLuint(origFramebuffer))

	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 CreateFromTexture(native NativeTexture, width, height int) *RenderTarget {
	framebuffer := createFramebuffer(C.GLuint(native))
	return &RenderTarget{framebuffer, width, height, false}
}

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) SetAsViewport() {
	current := C.GLint(0)
	C.glGetIntegerv(C.GL_FRAMEBUFFER_BINDING, &current)
	if C.GLuint(current) == r.framebuffer {
		return
	}
	r.setAsViewport()
}

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 {
		// Flip Y and move to fit with the top of the window.
		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)
}