Move rendering related functions out of compton.c

Moved:
* Blur kernel related functions to kernel.c
* Vsync related functions to vsync.c
* paint related functions to render.c

This will make the `split-backend` branch easier to rebase.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/kernel.c

@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
+
+#include <math.h>
+
+#include "utils.h"
+#include "kernel.h"
+
+/*
+ * A picture will help
+ *
+ *      -center   0                width  width+center
+ *  -center +-----+-------------------+-----+
+ *          |     |                   |     |
+ *          |     |                   |     |
+ *        0 +-----+-------------------+-----+
+ *          |     |                   |     |
+ *          |     |                   |     |
+ *          |     |                   |     |
+ *   height +-----+-------------------+-----+
+ *          |     |                   |     |
+ * height+  |     |                   |     |
+ *  center  +-----+-------------------+-----+
+ */
+
+double
+sum_kernel(conv *map, int x, int y, int width, int height) {
+	int fx, fy;
+	double *g_data;
+	double *g_line = map->data;
+	int g_size = map->size;
+	int center = g_size / 2;
+	int fx_start, fx_end;
+	int fy_start, fy_end;
+	double v;
+
+	/*
+	 * Compute set of filter values which are "in range",
+	 * that's the set with:
+	 *    0 <= x + (fx-center) && x + (fx-center) < width &&
+	 *  0 <= y + (fy-center) && y + (fy-center) < height
+	 *
+	 *  0 <= x + (fx - center)    x + fx - center < width
+	 *  center - x <= fx    fx < width + center - x
+	 */
+
+	fx_start = center - x;
+	if (fx_start < 0)
+		fx_start = 0;
+	fx_end = width + center - x;
+	if (fx_end > g_size)
+		fx_end = g_size;
+
+	fy_start = center - y;
+	if (fy_start < 0)
+		fy_start = 0;
+	fy_end = height + center - y;
+	if (fy_end > g_size)
+		fy_end = g_size;
+
+	g_line = g_line + fy_start * g_size + fx_start;
+
+	v = 0;
+
+	for (fy = fy_start; fy < fy_end; fy++) {
+		g_data = g_line;
+		g_line += g_size;
+
+		for (fx = fx_start; fx < fx_end; fx++) {
+			v += *g_data++;
+		}
+	}
+
+	if (v > 1)
+		v = 1;
+
+	return v;
+}
+
+static double __attribute__((const)) gaussian(double r, double x, double y) {
+	// Formula can be found here:
+	// https://en.wikipedia.org/wiki/Gaussian_blur#Mathematics
+	// Except a special case for r == 0 to produce sharp shadows
+	if (r == 0)
+		return 1;
+	return exp(-0.5 * (x * x + y * y) / (r * r)) / (2 * M_PI * r * r);
+}
+
+conv *gaussian_kernel(double r) {
+	conv *c;
+	int size = r * 2 + 1;
+	int center = size / 2;
+	double t;
+
+	c = cvalloc(sizeof(conv) + size * size * sizeof(double));
+	c->size = size;
+	t = 0.0;
+
+	/*printf_errf("(): %f", r);*/
+	for (int y = 0; y < size; y++) {
+		for (int x = 0; x < size; x++) {
+			double g = gaussian(r, x - center, y - center);
+			t += g;
+			c->data[y * size + x] = g;
+			/*printf("%f ", c->data[y*size+x]);*/
+		}
+		/*printf("\n");*/
+	}
+
+	for (int y = 0; y < size; y++) {
+		for (int x = 0; x < size; x++) {
+			c->data[y * size + x] /= t;
+			/*printf("%f ", c->data[y*size+x]);*/
+		}
+		/*printf("\n");*/
+	}
+
+	return c;
+}
+
+// vim: set noet sw=8 ts=8 :