lighttroupe/luz

#
# GLFrameBufferObject is an off-screen chunk of video memory that we can render into, and use as a texture for further rendering.
#
require 'drawing'

class GLFrameBufferObject
    include Drawing

    attr_reader :image, :height, :width

    def initialize(settings={})
        @width, @height = (settings[:width] || 1024), (settings[:height] || 768)        # TODO: use screen resolution
        @clear_color = [0.0, 0.0, 0.0, 0.0]
        create
    end

private

    def create
        @fbo = GL.GenFramebuffersEXT(1).first

        # Bind it
        GL.BindFramebufferEXT(GL::FRAMEBUFFER_EXT, @fbo)

        #GL.RenderbufferStorageEXT(GL::RENDERBUFFER_EXT, GL::RGBA, @width, @height)

        # create texture to render into
        @image = GL.GenTexture
        GL.BindTexture(GL::TEXTURE_2D, @image)

        #
        # GL_CLAMP, GL_CLAMP_TO_BORDER, GL_CLAMP_TO_EDGE, GL_MIRRORED_REPEAT, or GL_REPEAT (default)
        # (MIRRORED_REPEAT flips a basic Image of Previous Frame vertically)
        #
        GL.TexParameter(GL::TEXTURE_2D, GL::TEXTURE_WRAP_S, GL::REPEAT)        # REPEAT mode adds noise to the transparent edge of a texture opposite an opaque edge
        GL.TexParameter(GL::TEXTURE_2D, GL::TEXTURE_WRAP_T, GL::REPEAT)

        GL.TexParameter(GL::TEXTURE_2D, GL::TEXTURE_MAG_FILTER, GL::LINEAR) # or GL::NEAREST
        GL.TexParameter(GL::TEXTURE_2D, GL::TEXTURE_MIN_FILTER, GL::LINEAR) # or GL::NEAREST

        GL.TexImage2D(GL::TEXTURE_2D, 0, GL::RGBA8, @width, @height, 0, GL::RGBA, GL::UNSIGNED_BYTE, nil)

        # attach texture to FBO
        GL.FramebufferTexture2DEXT(GL::FRAMEBUFFER_EXT, GL::COLOR_ATTACHMENT0_EXT, GL::TEXTURE_2D, @image, 0)

        #
        # Depth buffer
        #
        #@depth_buffer = GL.GenRenderbuffersEXT(1).first
        #GL.BindRenderbufferEXT(GL::RENDERBUFFER_EXT, @depth_buffer)
        #GL.RenderbufferStorageEXT(GL::RENDERBUFFER_EXT, GL::DEPTH_COMPONENT, @width, @height)
        #GL.BindRenderbufferEXT(GL::RENDERBUFFER_EXT, 0)
        #GL.FramebufferRenderbufferEXT(GL::FRAMEBUFFER_EXT, GL::DEPTH_ATTACHMENT_EXT, GL::RENDERBUFFER_EXT, @depth_buffer)

        # check status
        if (status = GL.CheckFramebufferStatusEXT(GL::FRAMEBUFFER_EXT)) != GL::FRAMEBUFFER_COMPLETE_EXT
            puts "framebuffer creation failed (status: #{status})"
        end
        GL.BindFramebufferEXT(GL::FRAMEBUFFER_EXT, 0)
    end

public

    $fbo_stack ||= []
    def using(options={})
        $fbo_stack << @fbo

        # Switch rendering to FBO
        GL.BindFramebufferEXT(GL::FRAMEBUFFER_EXT, @fbo)

        GL.PushAttrib(GL::VIEWPORT_BIT)
        GL.Viewport(0, 0, @width, @height)

        with_identity_transformation {
            clear_screen(@clear_color) unless options[:clear] === false
            yield
        }

        GL.PopAttrib
        $fbo_stack.pop
        GL.BindFramebufferEXT(GL::FRAMEBUFFER_EXT, $fbo_stack.last || 0)
    end

    def with_image(&proc)
        with_texture_scale(1.0, -1.0) {        # texture coordinates seem to need to be flipped vertically with FBOs
            with_texture(@image, &proc)
        }
    end
end