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;;; Chickadee Game Toolkit
;;; Copyright © 2017 David Thompson <davet@gnu.org>
;;;
;;; Chickadee is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published
;;; by the Free Software Foundation, either version 3 of the License,
;;; or (at your option) any later version.
;;;
;;; Chickadee is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Viewports specify the renderable section of a window.
;;
;;; Code:
(define-module (chickadee render viewport)
#:use-module (ice-9 match)
#:use-module (srfi srfi-9)
#:use-module (gl)
#:use-module (chickadee utils)
#:use-module (chickadee render gl)
#:use-module (chickadee render gpu)
#:use-module (chickadee color)
#:export (make-viewport
viewport?
viewport-x
viewport-y
viewport-width
viewport-height
viewport-clear-color
viewport-clear-flags
null-viewport
%default-clear-flags
%default-clear-color
apply-viewport
*viewport-state*))
(define-record-type <viewport>
(%make-viewport x y width height clear-color clear-flags)
viewport?
(x viewport-x)
(y viewport-y)
(width viewport-width)
(height viewport-height)
(clear-color viewport-clear-color)
(clear-flags viewport-clear-flags))
(define %default-clear-flags '(color-buffer depth-buffer))
;; Just a fun color from the Dawnbringer 32-color palette instead of
;; boring old black.
(define %default-clear-color (rgb #x45283c))
(define (assert-non-negative-integer n)
(if (and (integer? n) (>= n 0))
n
(error "expecting non-negative integer:" n)))
(define* (make-viewport x y width height #:key
(clear-color %default-clear-color)
(clear-flags %default-clear-flags))
"Create a viewport that covers an area of the window starting from
coordinates (X, Y) and spanning WIDTH x HEIGHT pixels. Fill the
viewport with CLEAR-COLOR when clearing the screen. Clear the buffers
denoted by the list of symbols in CLEAR-FLAGS. Possible values for
CLEAR-FLAGS are 'color-buffer', 'depth-buffer', 'accum-buffer', and
'stencil-buffer'."
(%make-viewport (assert-non-negative-integer x)
(assert-non-negative-integer y)
(assert-non-negative-integer width)
(assert-non-negative-integer height)
clear-color
clear-flags))
(define null-viewport (make-viewport 0 0 0 0))
(define clear-buffer-mask
(memoize
(lambda (flags)
(apply logior
;; Map symbols to OpenGL constants.
(map (match-lambda
('depth-buffer 256)
('accum-buffer 512)
('stencil-buffer 1024)
('color-buffer 16384))
flags)))))
(define (apply-viewport viewport)
"Set the OpenGL state for VIEWPORT. Clip rendering to the viewport
area, set the clear color, and clear necessary buffers."
(unless (eq? viewport null-viewport)
(let ((x (viewport-x viewport))
(y (viewport-y viewport))
(w (viewport-width viewport))
(h (viewport-height viewport))
(c (viewport-clear-color viewport)))
(gl-enable (enable-cap scissor-test))
(gl-viewport x y w h)
(gl-scissor x y w h)
(gl-clear-color (color-r c) (color-g c) (color-b c) (color-a c))
(gl-clear (clear-buffer-mask (viewport-clear-flags viewport))))))
(define *viewport-state*
(make-gpu-state apply-viewport null-viewport))
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