FEAT: new blur native function for fast Gaussian blur of images

Based on Ivan Kuckir's Fastest Gaussian blur implementation algorithm from article: http://blog.ivank.net/fastest-gaussian-blur.html Usage example: ``` image: load %some-image.jpg blur image 15 ;@@ image is modified! save %blured-image.png image ```
Oldes · Jun 29, 2021 · c756498 · c756498
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diff --git a/make/rebol3.nest b/make/rebol3.nest
@@ -313,11 +313,12 @@ config: [ ;- this is list of configuration (optional) defines
 ;- image related natives and codecs:                                            
 include-image-natives: [
 	; image related native functions like:
-	; `hsv-to-rgb`, `rgb-to-hsv`, `tint`, `resize`, `premultiply`
+	; `hsv-to-rgb`, `rgb-to-hsv`, `tint`, `resize`, `premultiply`, `blur`
 	; on Windows also: `image` as common entry to os image codec (if enabled)
 	config: INCLUDE_IMAGE_NATIVES
 	core-files: %core/n-image.c
 	core-files: %core/u-image-resize.c
+	core-files: %core/u-image-blur.c
 ]
 
 include-native-bmp-codec: [config: INCLUDE_BMP_CODEC core-files: %core/u-bmp.c]

diff --git a/src/core/n-image.c b/src/core/n-image.c
@@ -3,7 +3,7 @@
 **  REBOL [R3] Language Interpreter and Run-time Environment
 **
 **  Copyright 2012 REBOL Technologies
-**  Copyright 2012-2019 Rebol Open Source Contributors
+**  Copyright 2012-2021 Rebol Open Source Contributors
 **  REBOL is a trademark of REBOL Technologies
 **
 **  Licensed under the Apache License, Version 2.0 (the "License");
@@ -34,6 +34,7 @@
 
 #include "reb-codec.h"
 #include "sys-magick.h" // used for `resize` native
+#include "sys-blur.h" // used for `blur` native
 #if defined(TO_WINDOWS) && defined(INCLUDE_IMAGE_OS_CODEC)
 #include "winerror.h" // used for WINCODEC_ERR_COMPONENTNOTFOUND
 #endif
@@ -339,6 +340,25 @@ typedef struct REBCLR {
 	return R_ARG1;
 }
 
+/***********************************************************************
+**
+*/	REBNATIVE(blur)
+/*
+//	blur: native [
+//		"Blur (Gaussian) given image"
+//		 image    [image!]  "Image to blur (modified)"
+//		 radius   [number!] "Blur amount"
+//	]
+***********************************************************************/
+{
+	REBVAL* val_img = D_ARG(1);
+	REBVAL* val_rad = D_ARG(2);
+	REBINT radius = IS_INTEGER(val_rad) ? VAL_INT32(val_rad) : (REBINT)round(VAL_DECIMAL(val_rad));
+
+	BlurImage(VAL_SERIES(val_img), radius);
+	return R_ARG1;
+}
+
 /***********************************************************************
 **
 */	REBNATIVE(image)

diff --git a/src/core/u-image-blur.c b/src/core/u-image-blur.c
@@ -0,0 +1,203 @@
+/***********************************************************************
+**
+**  REBOL [R3] Language Interpreter and Run-time Environment
+**
+**  Copyright 2012 REBOL Technologies
+**  Copyright 2012-2021 Rebol Open Source Developers
+**  REBOL is a trademark of REBOL Technologies
+**
+**  Licensed under the Apache License, Version 2.0 (the "License");
+**  you may not use this file except in compliance with the License.
+**  You may obtain a copy of the License at
+**
+**  http://www.apache.org/licenses/LICENSE-2.0
+**
+**  Unless required by applicable law or agreed to in writing, software
+**  distributed under the License is distributed on an "AS IS" BASIS,
+**  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+**  See the License for the specific language governing permissions and
+**  limitations under the License.
+**
+************************************************************************
+**
+**  Module:  u-image-blur.c
+**  Summary: image blur
+**  Section: utility
+**  Author:  Oldes
+** 
+**  Note:
+**  Based on Ivan Kuckir's Fastest Gaussian blur implementation algorithm
+**  from article: http://blog.ivank.net/fastest-gaussian-blur.html and
+**  SilverWin's C port of it: https://github.com/SilverWin/blur_lib
+**
+***********************************************************************/
+
+#include "sys-core.h"
+
+#ifdef INCLUDE_IMAGE_NATIVES
+#include "sys-blur.h"
+
+static void boxes_for_gauss(REBDEC sigma, REBINT sizes[3])
+{
+	REBDEC wIdeal;
+	REBINT wl;
+	REBINT wu;
+	REBDEC mIdeal;
+	REBINT m;
+	REBINT n = 3;
+
+	wIdeal = sqrt((REBDEC)(12 * sigma * sigma / n) + 1); /* Ideal averaging filter width */
+	wl = (REBINT)floor(wIdeal);
+	if (wl % 2 == 0)
+		wl--;
+	wu = wl + 2;
+
+	mIdeal = (12 * sigma * sigma - (REBDEC)wl * wl * n - 4.0 * n * wl - 3.0 * n) / (-4.0 * wl - 4);
+	m = (REBINT)round(mIdeal);
+
+	for (REBINT i = 0; i < n; i++)
+	{
+		if (i < m)
+		{
+			sizes[i] = wl;
+		}
+		else
+		{
+			sizes[i] = wu;
+		}
+	}
+}
+
+static void box_blur_H(REBYTE *scl, REBYTE*tcl, REBINT w, REBINT h, REBINT r, REBINT bpp)
+{
+	for (REBINT i = 0; i < h; i++)
+	{
+		for (REBINT k = 0; k < bpp; k++)
+		{
+			REBINT ti = i * w * bpp + k;
+			REBINT li = ti;
+			REBINT ri = ti + r * bpp;
+			REBINT fv = scl[li];
+			REBINT lv = scl[ti + (w - 1) * bpp];
+			REBINT val = (r + 1) * fv;
+			for (REBINT j = 0; j < r; j++)
+			{
+				val += scl[ti + (j * bpp)];
+			}
+			for (REBINT j = 0; j <= r; j++)
+			{
+				val += scl[ri] - fv;
+				tcl[ti] = (REBYTE)round(val / (r + r + 1));
+				ri += bpp;
+				ti += bpp;
+			}
+			for (REBINT j = r + 1; j < (w - r); j++)
+			{
+				val += scl[ri] - scl[li];
+				tcl[ti] = (REBYTE)round(val / (r + r + 1));
+				li += bpp;
+				ri += bpp;
+				ti += bpp;
+			}
+			for (REBINT j = w - r; j < w; j++)
+			{
+				val += lv - scl[li];
+				tcl[ti] = (REBYTE)round(val / (r + r + 1));
+				li += bpp;
+				ti += bpp;
+			}
+		}
+	}
+}
+
+static void box_blur_T(REBYTE*scl, REBYTE*tcl, REBINT w, REBINT h, REBINT r, REBINT bpp)
+{
+	REBINT i, j, k, ti, li, ri, fv, lv, val;
+	for (i = 0; i < w; i++)
+	{
+		for (k = 0; k < bpp; k++)
+		{
+			ti = i * bpp + k;
+			li = ti;
+			ri = ti + r * w * bpp;
+			fv = scl[ti];
+			lv = scl[ti + w * (h - 1) * bpp];
+			val = (r + 1) * fv;
+			for (j = 0; j < r; j++)
+			{
+				val += scl[ti + j * w * bpp];
+			}
+			for (j = 0; j <= r; j++)
+			{
+				val += scl[ri] - fv;
+				tcl[ti] = (REBYTE)round(val / (r + r + 1));
+				ri += w * bpp;
+				ti += w * bpp;
+			}
+			for (j = r + 1; j < (h - r); j++)
+			{
+				val += scl[ri] - scl[li];
+				tcl[ti] = (REBYTE)round(val / (r + r + 1));
+				li += w * bpp;
+				ri += w * bpp;
+				ti += w * bpp;
+			}
+			for (j = h - r; j < h; j++)
+			{
+				val += lv - scl[li];
+				tcl[ti] = (REBYTE)round(val / (r + r + 1));
+				li += w * bpp;
+				ti += w * bpp;
+			}
+		}
+	}
+}
+
+static void box_blur(REBYTE*scl, REBYTE*tcl, REBINT w, REBINT h, REBINT r, REBINT bpp)
+{
+	for (REBINT i = 0; i < (h * w * bpp); i++)
+	{
+		tcl[i] = scl[i];
+	}
+	box_blur_H(tcl, scl, w, h, r, bpp);
+	box_blur_T(scl, tcl, w, h, r, bpp);
+}
+
+void fast_gauss_blur(REBYTE*scl, REBYTE*tcl, REBINT w, REBINT h, REBINT r, REBINT bpp)
+{
+	REBINT bxs[3];
+	boxes_for_gauss(r, bxs);
+	box_blur(scl, tcl, w, h, (bxs[0] - 1) / 2, bpp);
+	box_blur(tcl, scl, w, h, (bxs[1] - 1) / 2, bpp);
+	box_blur(scl, tcl, w, h, (bxs[2] - 1) / 2, bpp);
+	// result would be in tcl, so copy it back to source, as it is modified anyway
+	for (REBINT i = 0; i < (h * w * bpp); i++)
+	{
+		scl[i] = tcl[i];
+	}
+}
+
+void BlurImage(REBSER *image, REBINT radius)
+{
+	REBSER *temp_image;
+
+	// Validate input.
+	if ( image == NULL
+		|| (IMG_WIDE(image) == 0UL)
+		|| (IMG_HIGH(image) == 0UL)
+		|| radius <= 0
+	) return;
+
+	radius = MIN(radius, IMG_WIDE(image) / 2);
+	radius = MIN(radius, IMG_HIGH(image) / 2);
+
+	// Prepare temporary image.
+
+	temp_image = Make_Image(IMG_WIDE(image), IMG_HIGH(image), TRUE);
+
+	// Resize image.
+
+	fast_gauss_blur(IMG_DATA(image), IMG_DATA(temp_image), IMG_WIDE(image), IMG_HIGH(image), radius, 4);
+}
+
+#endif // INCLUDE_IMAGE_NATIVES
diff --git a/src/include/sys-blur.h b/src/include/sys-blur.h
@@ -0,0 +1,6 @@
+#ifndef __INCLUDE_BLUR_H__
+#define __INCLUDE_BLUR_H__
+
+void BlurImage(REBSER *image, REBINT radius);
+
+#endif
diff --git a/src/tests/units/files/flower.png b/src/tests/units/files/flower.png
diff --git a/src/tests/units/image-test.r3 b/src/tests/units/image-test.r3
@@ -330,6 +330,33 @@ FFFFFFDC1616212121212121
 ===end-group===
 
 
+===start-group=== "BLUR"
+if value? 'blur [
+--test--  "blur"
+	i: load %units/files/flower.png
+	c: checksum to binary! i 'crc32
+	t: copy i
+	--assert all [
+		image? blur t 0
+		c = checksum to binary! t 'crc32
+	]
+	--assert all [
+		image? blur t 5
+		-1700743341 = checksum to binary! t 'crc32
+	]
+	--assert all [
+		image? blur t 5
+		-583506697  = checksum to binary! t 'crc32
+	]
+	--assert all [
+		image? blur i 100000
+		1523895462  = checksum to binary! i 'crc32
+	]
+	t: i: none
+]
+===end-group===
+
+
 ===start-group=== "Save/load image"
 	if find codecs 'png [
 		--test-- "save/load PNG"