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Add comments explaining how the blurring works

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Alexander van Gessel 2017-11-05 15:44:58 +01:00 • committed by Charles Dang
parent cd886048dc
commit 403a45ecf4
1 changed files with 18 additions and 0 deletions
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18
src/sdl/utils.cpp
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@ -1609,8 +1609,12 @@ surface blur_alpha_surface(const surface &surf, int depth)
surface_lock lock(res);
int x, y;
// Iterate over rows, blurring each row horizontally
for(y = 0; y < res->h; ++y) {
// Sum of pixel values stored here
Uint32 alpha=0, red = 0, green = 0, blue = 0;
// Preload the first depth+1 pixels
Uint32* p = lock.pixels() + y*res->w;
for(x = 0; x <= depth && x < res->w; ++x, ++p) {
alpha += ((*p) >> 24)&0xFF;
@ -1621,10 +1625,14 @@ surface blur_alpha_surface(const surface &surf, int depth)
queue.push_back(*p);
}
// This is the actual inner loop
p = lock.pixels() + y*res->w;
for(x = 0; x < res->w; ++x, ++p) {
// Write the current average
const Uint32 num = queue.size();
*p = (std::min(alpha/num,ff) << 24) | (std::min(red/num,ff) << 16) | (std::min(green/num,ff) << 8) | std::min(blue/num,ff);
// Unload earlier pixels that are now too far away
if(x >= depth) {
{
const auto &front = queue.front();
@ -1637,6 +1645,7 @@ surface blur_alpha_surface(const surface &surf, int depth)
queue.pop_front();
}
// Add new pixels
if(x + depth+1 < res->w) {
Uint32* q = p + depth+1;
alpha += ((*q) >> 24)&0xFF;
@ -1651,8 +1660,12 @@ surface blur_alpha_surface(const surface &surf, int depth)
queue.clear();
}
// Iterate over columns, blurring each column vertically
for(x = 0; x < res->w; ++x) {
// Sum of pixel values stored here
Uint32 alpha=0, red = 0, green = 0, blue = 0;
// Preload the first depth+1 pixels
Uint32* p = lock.pixels() + x;
for(y = 0; y <= depth && y < res->h; ++y, p += res->w) {
alpha += ((*p) >> 24)&0xFF;
@ -1663,10 +1676,14 @@ surface blur_alpha_surface(const surface &surf, int depth)
queue.push_back(*p);
}
// This is the actual inner loop
p = lock.pixels() + x;
for(y = 0; y < res->h; ++y, p += res->w) {
// Write the current average
const Uint32 num = queue.size();
*p = (std::min(alpha/num,ff) << 24) | (std::min(red/num,ff) << 16) | (std::min(green/num,ff) << 8) | std::min(blue/num,ff);
// Unload earlier pixels that are now too far away
if(y >= depth) {
{
const auto &front = queue.front();
@ -1679,6 +1696,7 @@ surface blur_alpha_surface(const surface &surf, int depth)
queue.pop_front();
}
// Add new pixels
if(y + depth+1 < res->h) {
Uint32* q = p + (depth+1)*res->w;
alpha += ((*q) >> 24)&0xFF;