Add blend mode bindings.

1 files changed, 139 insertions, 0 deletions

diff --git a/sdl2/blend-mode.scm b/sdl2/blend-mode.scm
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--- /dev/null
+++ b/sdl2/blend-mode.scm
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+;;; guile-sdl2 --- FFI bindings for SDL2
+;;; Copyright © 2020 Leo Prikler <leo.prikler@student.tugraz.at>
+;;; Copyright © 2020 David Thompson <davet@gnu.org>
+;;;
+;;; This file is part of guile-sdl2.
+;;;
+;;; Guile-sdl2 is free software; you can redistribute it and/or modify
+;;; it under the terms of the GNU Lesser General Public License as
+;;; published by the Free Software Foundation; either version 3 of the
+;;; License, or (at your option) any later version.
+;;;
+;;; Guile-sdl2 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 Lesser General Public
+;;; License along with guile-sdl2.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+(define-module (sdl2 blend-mode)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-9)
+  #:use-module (sdl2)
+  #:use-module ((sdl2 bindings) #:prefix ffi:)
+  #:export (make-blend-mode
+            blend-mode?
+            blend-mode-src-color-factor
+            blend-mode-dst-color-factor
+            blend-mode-color-operation
+            blend-mode-src-alpha-factor
+            blend-mode-dst-alpha-factor
+            blend-mode-alpha-operation
+            none
+            blend
+            add
+            mod
+            mul))
+
+(define-record-type <blend-mode>
+  (%make-blend-mode src-color-factor dst-color-factor color-operation
+                    src-alpha-factor dst-alpha-factor alpha-operation
+                    bitmask)
+  blend-mode?
+  (src-color-factor blend-mode-src-color-factor)
+  (dst-color-factor blend-mode-dst-color-factor)
+  (color-operation  blend-mode-color-operation)
+  (src-alpha-factor blend-mode-src-alpha-factor)
+  (dst-alpha-factor blend-mode-dst-alpha-factor)
+  (alpha-operation  blend-mode-alpha-operation)
+  (bitmask blend-mode-bitmask))
+
+(define none
+  (%make-blend-mode 'one 'zero 'add 'one 'zero 'add
+                    ffi:SDL_BLENDMODE_NONE))
+
+(define blend
+  (%make-blend-mode 'src-alpha 'one-minus-src-alpha 'add
+                    'one       'one-minus-src-alpha 'add
+                    ffi:SDL_BLENDMODE_BLEND))
+
+(define add
+  (%make-blend-mode 'src-alpha 'one 'add
+                    'zero      'one 'add
+                    ffi:SDL_BLENDMODE_ADD))
+
+(define mod
+  (%make-blend-mode 'zero 'src-color 'add
+                    'zero 'one       'add
+                    ffi:SDL_BLENDMODE_MOD))
+
+(define mul
+  (%make-blend-mode 'dst-color 'one-minus-src-alpha 'add
+                    'dst-alpha 'one-minus-src-alpha 'add
+                    ffi:SDL_BLENDMODE_MUL))
+
+(define (make-blend-mode src-color-factor dst-color-factor color-operation
+                         src-alpha-factor dst-alpha-factor alpha-operation)
+  "Return a new custom blend mode for renderers.
+
+SRC-COLOR-FACTOR applies to the red, green, and blue components of the
+source pixels.
+
+DST-COLOR-FACTOR applies to the red, green, and blue components of the
+destination pixels.
+
+COLOR-OPERATION specifies how to combine the red, green, and blue
+components of the source and destination pixels.
+
+SRC-ALPHA-FACTOR applies to the alpha component of the source pixels.
+
+DST-ALPHA-FACTOR applies to the alpha component of the destination
+pixels.
+
+ALPHA-OPERATION specifies how to combine the alpha component of the
+source and destination pixels.
+
+Possible values for factors are zero, one, src-color,
+one-minus-src-color, src-alpha, one-minus-src-alpha, dst-color,
+one-minus-dst-color, dst-alpha, and one-minus-dst alpha.
+
+Possible values for operations are add, subtract, rev-subtract,
+minimum, and maximum."
+  (define symbol->blend-operation
+    (match-lambda
+      ('add          ffi:SDL_BLENDOPERATION_ADD)
+      ('subtract     ffi:SDL_BLENDOPERATION_SUBTRACT)
+      ('rev-subtract ffi:SDL_BLENDOPERATION_REV_SUBTRACT)
+      ('minimum      ffi:SDL_BLENDOPERATION_MINIMUM)
+      ('maximum      ffi:SDL_BLENDOPERATION_MAXIMUM)))
+  (define symbol->blend-factor
+    (match-lambda
+      ('zero                ffi:SDL_BLENDFACTOR_ZERO)
+      ('one                 ffi:SDL_BLENDFACTOR_ONE)
+      ('src-color           ffi:SDL_BLENDFACTOR_SRC_COLOR)
+      ('one-minus-src-color ffi:SDL_BLENDFACTOR_ONE_MINUS_SRC_COLOR)
+      ('src-alpha           ffi:SDL_BLENDFACTOR_SRC_ALPHA)
+      ('one-minus-src-alpha ffi:SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA)
+      ('dst-color           ffi:SDL_BLENDFACTOR_DST_COLOR)
+      ('one-minus-dst-color ffi:SDL_BLENDFACTOR_ONE_MINUS_DST_COLOR)
+      ('dst-alpha           ffi:SDL_BLENDFACTOR_DST_ALPHA)
+      ('one-minus-dst-alpha ffi:SDL_BLENDFACTOR_ONE_MINUS_DST_ALPHA)))
+  (let ((bitmask (ffi:sdl-compose-custom-blend-mode
+                  (symbol->blend-factor src-color-factor)
+                  (symbol->blend-factor dst-color-factor)
+                  (symbol->blend-operation color-operation)
+                  (symbol->blend-factor src-alpha-factor)
+                  (symbol->blend-factor dst-alpha-factor)
+                  (symbol->blend-operation alpha-operation))))
+    (if (eq? bitmask ffi:SDL_BLENDMODE_INVALID)
+        (sdl-error "make-blend-mode"
+                   "invalid custom blend mode")
+        (%make-blend-mode src-color-factor
+                          dst-color-factor
+                          color-operation
+                          src-alpha-factor
+                          dst-alpha-factor
+                          alpha-operation
+                          bitmask))))