fix(blur): use rendered surface after commit

- Fix blur logic
- Reused rendered surface to optimize future render on comitted blur
- Include gaussian kernel function

Closes #20
Closes #22

include/algebra.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <glib.h>
+
+struct gaussian_kernel {
+  gdouble *kernel;
+  gint size;
+  gdouble sigma;
+  gdouble sum;
+};
+
+struct gaussian_kernel *gaussian_kernel(gint width, gdouble sigma);
+void gaussian_kernel_free(gpointer data);

include/swappy.h

@@ -79,9 +79,10 @@ struct swappy_paint_brush {
 };
 
 struct swappy_paint_blur {
-  double bluriness;
+  double blur_level;
   struct swappy_point from;
   struct swappy_point to;
+  cairo_surface_t *surface;
 };
 
 struct swappy_paint {

include/util.h

@@ -4,4 +4,5 @@
 #include <glib.h>
 
 void string_remove_at(char *str, size_t pos);
-gchar *string_insert_chars_at(gchar *str, gchar *chars, size_t pos);
+gchar *string_insert_chars_at(gchar *str, gchar *chars, size_t pos);
+void pixel_data_print(guint32 pixel);

meson.build

@@ -51,6 +51,7 @@ executable(
 	swappy_resources,
 	files([
 		'src/main.c',
+		'src/algebra.c',
 		'src/application.c',
 		'src/buffer.c',
 		'src/box.c',

src/algebra.c

@@ -0,0 +1,37 @@
+#include "algebra.h"
+
+#include <glib.h>
+#include <math.h>
+
+struct gaussian_kernel *gaussian_kernel(int width, double sigma) {
+  double sum = 0;
+  gint size = width * width + 1;
+  double *kernel = g_new(double, size);
+  struct gaussian_kernel *gaussian = g_new(struct gaussian_kernel, 1);
+  for (gint y = 0; y < width; y++) {
+    for (gint x = 0; x < width; x++) {
+      double j = y - width;
+      double i = x - width;
+      double cell = ((1.0 / (2.0 * G_PI * sigma)) *
+                     exp((-(i * i + j * j)) / (2.0 * sigma * sigma))) *
+                    0xff;
+      kernel[y * width + x] = cell;
+      sum += cell;
+    }
+  }
+
+  gaussian->kernel = kernel;
+  gaussian->size = size;
+  gaussian->sigma = sigma;
+  gaussian->sum = sum;
+
+  return gaussian;
+}
+
+void gaussian_kernel_free(gpointer data) {
+  struct gaussian_kernel *gaussian = (struct gaussian_kernel *)data;
+  if (gaussian != NULL) {
+    g_free(gaussian->kernel);
+    g_free(gaussian);
+  }
+}

src/application.c

@@ -406,11 +406,18 @@ gboolean draw_area_configure_handler(GtkWidget *widget,
   g_debug("received configure_event handler");
   cairo_surface_destroy(state->cairo_surface);
 
-  state->cairo_surface = gdk_window_create_similar_surface(
-      gtk_widget_get_window(widget), CAIRO_CONTENT_COLOR,
+  cairo_surface_t *surface = gdk_window_create_similar_surface(
+      gtk_widget_get_window(widget), CAIRO_CONTENT_COLOR_ALPHA,
       gtk_widget_get_allocated_width(widget),
       gtk_widget_get_allocated_height(widget));
 
+  g_info("size of cairo_surface: %ux%u with type: %d",
+         cairo_image_surface_get_width(surface),
+         cairo_image_surface_get_height(surface),
+         cairo_image_surface_get_format(surface));
+
+  state->cairo_surface = surface;
+
   render_state(state);
 
   return TRUE;

src/paint.c

@@ -23,6 +23,9 @@ void paint_free(gpointer data) {
 
   switch (paint->type) {
     case SWAPPY_PAINT_MODE_BLUR:
+      if (paint->content.blur.surface) {
+        cairo_surface_destroy(paint->content.blur.surface);
+      }
       break;
     case SWAPPY_PAINT_MODE_BRUSH:
       g_list_free_full(paint->content.brush.points, g_free);
@@ -70,7 +73,7 @@ void paint_add_temporary(struct swappy_state *state, double x, double y,
     if (type == SWAPPY_PAINT_MODE_TEXT) {
       paint_commit_temporary(state);
     } else {
-      g_free(state->temp_paint);
+      paint_free(state->temp_paint);
       state->temp_paint = NULL;
     }
   }
@@ -79,9 +82,10 @@ void paint_add_temporary(struct swappy_state *state, double x, double y,
     case SWAPPY_PAINT_MODE_BLUR:
       paint->can_draw = false;
 
-      paint->content.blur.bluriness = state->settings.blur_level;
+      paint->content.blur.blur_level = state->settings.blur_level;
       paint->content.blur.from.x = x;
       paint->content.blur.from.y = y;
+      paint->content.blur.surface = NULL;
       break;
     case SWAPPY_PAINT_MODE_BRUSH:
       paint->can_draw = true;
@@ -147,6 +151,14 @@ void paint_update_temporary_shape(struct swappy_state *state, double x,
     return;
   }
 
+  int32_t width = state->window->width;
+  int32_t height = state->window->height;
+
+  // Bounding x and y to the window dimensions to avoid side effects in
+  // rendering.
+  x = fmin(fmax(x, 0), width);
+  y = fmin(fmax(y, 0), height);
+
   switch (paint->type) {
     case SWAPPY_PAINT_MODE_BLUR:
       paint->can_draw = true;