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diff --git a/app/operations/layer-modes/gimpoperationlayermode-composite.c b/app/operations/layer-modes/gimpoperationlayermode-composite.c
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+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * gimpoperationlayermode-composite.c
+ * Copyright (C) 2017 Michael Natterer <mitch@gimp.org>
+ * 2017 Øyvind Kolås <pippin@gimp.org>
+ * 2017 Ell
+ *
+ * This program 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.
+ *
+ * This program 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 <https://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include <gegl-plugin.h>
+#include <cairo.h>
+#include <gdk-pixbuf/gdk-pixbuf.h>
+
+#include "../operations-types.h"
+
+#include "gimpoperationlayermode-composite.h"
+
+
+/* non-subtractive compositing functions. these functions expect comp[ALPHA]
+ * to be the same as layer[ALPHA]. when in[ALPHA] or layer[ALPHA] are zero,
+ * the value of comp[RED..BLUE] is unconstrained (in particular, it may be
+ * NaN).
+ */
+
+
+void
+gimp_operation_layer_mode_composite_union (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat new_alpha;
+ gfloat in_alpha = in[ALPHA];
+ gfloat layer_alpha = layer[ALPHA] * opacity;
+
+ if (mask)
+ layer_alpha *= *mask;
+
+ new_alpha = layer_alpha + (1.0f - layer_alpha) * in_alpha;
+
+ if (layer_alpha == 0.0f || new_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else if (in_alpha == 0.0f)
+ {
+ out[RED] = layer[RED];
+ out[GREEN] = layer[GREEN];
+ out[BLUE] = layer[BLUE];
+ }
+ else
+ {
+ gfloat ratio = layer_alpha / new_alpha;
+ gint b;
+
+ for (b = RED; b < ALPHA; b++)
+ out[b] = ratio * (in_alpha * (comp[b] - layer[b]) + layer[b] - in[b]) + in[b];
+ }
+
+ out[ALPHA] = new_alpha;
+
+ in += 4;
+ layer += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+void
+gimp_operation_layer_mode_composite_clip_to_backdrop (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat layer_alpha = comp[ALPHA] * opacity;
+
+ if (mask)
+ layer_alpha *= *mask;
+
+ if (in[ALPHA] == 0.0f || layer_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else
+ {
+ gint b;
+
+ for (b = RED; b < ALPHA; b++)
+ out[b] = comp[b] * layer_alpha + in[b] * (1.0f - layer_alpha);
+ }
+
+ out[ALPHA] = in[ALPHA];
+
+ in += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+void
+gimp_operation_layer_mode_composite_clip_to_layer (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat layer_alpha = layer[ALPHA] * opacity;
+
+ if (mask)
+ layer_alpha *= *mask;
+
+ if (layer_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else if (in[ALPHA] == 0.0f)
+ {
+ out[RED] = layer[RED];
+ out[GREEN] = layer[GREEN];
+ out[BLUE] = layer[BLUE];
+ }
+ else
+ {
+ gint b;
+
+ for (b = RED; b < ALPHA; b++)
+ out[b] = comp[b] * in[ALPHA] + layer[b] * (1.0f - in[ALPHA]);
+ }
+
+ out[ALPHA] = layer_alpha;
+
+ in += 4;
+ layer += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+void
+gimp_operation_layer_mode_composite_intersection (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat new_alpha = in[ALPHA] * comp[ALPHA] * opacity;
+
+ if (mask)
+ new_alpha *= *mask;
+
+ if (new_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else
+ {
+ out[RED] = comp[RED];
+ out[GREEN] = comp[GREEN];
+ out[BLUE] = comp[BLUE];
+ }
+
+ out[ALPHA] = new_alpha;
+
+ in += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+/* subtractive compositing functions. these functions expect comp[ALPHA] to
+ * specify the modified alpha of the overlapping content, as a fraction of the
+ * original overlapping content (i.e., an alpha of 1.0 specifies that no
+ * content is subtracted.) when in[ALPHA] or layer[ALPHA] are zero, the value
+ * of comp[RED..BLUE] is unconstrained (in particular, it may be NaN).
+ */
+
+void
+gimp_operation_layer_mode_composite_union_sub (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat in_alpha = in[ALPHA];
+ gfloat layer_alpha = layer[ALPHA] * opacity;
+ gfloat comp_alpha = comp[ALPHA];
+ gfloat new_alpha;
+
+ if (mask)
+ layer_alpha *= *mask;
+
+ new_alpha = in_alpha + layer_alpha -
+ (2.0f - comp_alpha) * in_alpha * layer_alpha;
+
+ if (layer_alpha == 0.0f || new_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else if (in_alpha == 0.0f)
+ {
+ out[RED] = layer[RED];
+ out[GREEN] = layer[GREEN];
+ out[BLUE] = layer[BLUE];
+ }
+ else
+ {
+ gfloat ratio = in_alpha / new_alpha;
+ gfloat layer_coeff = 1.0f / in_alpha - 1.0f;
+ gint b;
+
+ for (b = RED; b < ALPHA; b++)
+ out[b] = ratio * (layer_alpha * (comp_alpha * comp[b] + layer_coeff * layer[b] - in[b]) + in[b]);
+ }
+
+ out[ALPHA] = new_alpha;
+
+ in += 4;
+ layer += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+void
+gimp_operation_layer_mode_composite_clip_to_backdrop_sub (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat layer_alpha = layer[ALPHA] * opacity;
+ gfloat comp_alpha = comp[ALPHA];
+ gfloat new_alpha;
+
+ if (mask)
+ layer_alpha *= *mask;
+
+ comp_alpha *= layer_alpha;
+
+ new_alpha = 1.0f - layer_alpha + comp_alpha;
+
+ if (in[ALPHA] == 0.0f || comp_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else
+ {
+ gfloat ratio = comp_alpha / new_alpha;
+ gint b;
+
+ for (b = RED; b < ALPHA; b++)
+ out[b] = comp[b] * ratio + in[b] * (1.0f - ratio);
+ }
+
+ new_alpha *= in[ALPHA];
+
+ out[ALPHA] = new_alpha;
+
+ in += 4;
+ layer += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+void
+gimp_operation_layer_mode_composite_clip_to_layer_sub (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat in_alpha = in[ALPHA];
+ gfloat layer_alpha = layer[ALPHA] * opacity;
+ gfloat comp_alpha = comp[ALPHA];
+ gfloat new_alpha;
+
+ if (mask)
+ layer_alpha *= *mask;
+
+ comp_alpha *= in_alpha;
+
+ new_alpha = 1.0f - in_alpha + comp_alpha;
+
+ if (layer_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else if (in_alpha == 0.0f)
+ {
+ out[RED] = layer[RED];
+ out[GREEN] = layer[GREEN];
+ out[BLUE] = layer[BLUE];
+ }
+ else
+ {
+ gfloat ratio = comp_alpha / new_alpha;
+ gint b;
+
+ for (b = RED; b < ALPHA; b++)
+ out[b] = comp[b] * ratio + layer[b] * (1.0f - ratio);
+ }
+
+ new_alpha *= layer_alpha;
+
+ out[ALPHA] = new_alpha;
+
+ in += 4;
+ layer += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}
+
+void
+gimp_operation_layer_mode_composite_intersection_sub (const gfloat *in,
+ const gfloat *layer,
+ const gfloat *comp,
+ const gfloat *mask,
+ gfloat opacity,
+ gfloat *out,
+ gint samples)
+{
+ while (samples--)
+ {
+ gfloat new_alpha = in[ALPHA] * layer[ALPHA] * comp[ALPHA] * opacity;
+
+ if (mask)
+ new_alpha *= *mask;
+
+ if (new_alpha == 0.0f)
+ {
+ out[RED] = in[RED];
+ out[GREEN] = in[GREEN];
+ out[BLUE] = in[BLUE];
+ }
+ else
+ {
+ out[RED] = comp[RED];
+ out[GREEN] = comp[GREEN];
+ out[BLUE] = comp[BLUE];
+ }
+
+ out[ALPHA] = new_alpha;
+
+ in += 4;
+ layer += 4;
+ comp += 4;
+ out += 4;
+
+ if (mask)
+ mask++;
+ }
+}