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;;; Chickadee Game Toolkit
;;; Copyright © 2016, 2021 David Thompson <dthompson2@worcester.edu>
;;;
;;; 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/>.
(define-module (chickadee graphics blend)
#:use-module (chickadee graphics engine)
#:use-module (chickadee graphics gl)
#:use-module (gl)
#:use-module (ice-9 match)
#:use-module (srfi srfi-9)
#:export (make-blend-mode
blend-mode?
blend-mode-equation
blend-mode-source-function
blend-mode-destination-function
blend:alpha
blend:multiply
blend:subtract
blend:add
blend:lighten
blend:darken
blend:screen
blend:replace
g:blend-mode
current-blend-mode))
(define-record-type <blend-mode>
(make-blend-mode equation source-function destination-function)
blend-mode?
(equation blend-mode-equation)
(source-function blend-mode-source-function)
(destination-function blend-mode-destination-function))
(define blend:alpha
(make-blend-mode 'add 'source-alpha 'one-minus-source-alpha))
(define blend:multiply
(make-blend-mode 'add 'destination-color 'zero))
(define blend:subtract
(make-blend-mode 'reverse-subtract 'one 'zero))
(define blend:add
(make-blend-mode 'add 'one 'one))
(define blend:lighten
(make-blend-mode 'max 'one 'zero))
(define blend:darken
(make-blend-mode 'min 'one 'zero))
(define blend:screen
(make-blend-mode 'add 'one 'one-minus-source-color))
(define blend:replace
(make-blend-mode 'add 'one 'zero))
(define (bind-blend-mode blend-mode)
(if blend-mode
(begin
(gl-enable (enable-cap blend))
(gl-blend-equation
(match (blend-mode-equation blend-mode)
('add
(blend-equation-mode-ext func-add-ext))
('subtract
(blend-equation-mode-ext func-subtract-ext))
('reverse-subtract
(blend-equation-mode-ext func-reverse-subtract-ext))
('min
(blend-equation-mode-ext min-ext))
('max
(blend-equation-mode-ext max-ext))
('alpha-min
(blend-equation-mode-ext alpha-min-sgix))
('alpha-max
(blend-equation-mode-ext alpha-min-sgix))))
(gl-blend-func (match (blend-mode-source-function blend-mode)
('zero
(blending-factor-src zero))
('one
(blending-factor-src one))
('destination-color
(blending-factor-src dst-color))
('one-minus-destination-color
(blending-factor-src one-minus-dst-color))
('source-alpha-saturate
(blending-factor-src src-alpha-saturate))
('source-alpha
(blending-factor-src src-alpha))
('one-minus-source-alpha
(blending-factor-src one-minus-src-alpha))
('destination-alpha
(blending-factor-src dst-alpha))
('one-minus-destination-alpha
(blending-factor-src one-minus-dst-alpha))
('constant-color
(blending-factor-src constant-color-ext))
('one-minus-constant-color
(blending-factor-src one-minus-constant-color-ext))
('contstant-alpha
(blending-factor-src constant-alpha-ext))
('one-minus-constant-alpha
(blending-factor-src one-minus-constant-alpha-ext)))
(match (blend-mode-destination-function blend-mode)
('zero
(blending-factor-dest zero))
('one
(blending-factor-dest one))
('source-color
(blending-factor-dest src-color))
('one-minus-source-color
(blending-factor-dest one-minus-src-color))
('source-alpha
(blending-factor-dest src-alpha))
('one-minus-source-alpha
(blending-factor-dest one-minus-src-alpha))
('destination-alpha
(blending-factor-dest dst-alpha))
('one-minus-destination-alpha
(blending-factor-dest one-minus-dst-alpha))
('constant-color
(blending-factor-dest constant-color-ext))
('one-minus-constant-color
(blending-factor-dest one-minus-constant-color-ext))
('contstant-alpha
(blending-factor-dest constant-alpha-ext))
('one-minus-constant-alpha
(blending-factor-dest one-minus-constant-alpha-ext)))))
(gl-disable (enable-cap blend))))
(define-graphics-state g:blend-mode
current-blend-mode
#:default blend:replace
#:bind bind-blend-mode)
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