From 97420f13d896ef0dc4c956fcc89d5818769ced88 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Wed, 26 Jun 2019 19:33:39 +0200
Subject: [PATCH] scroll: let the render erase the scrolled up region

The grid scroll operation no longer inserts a DAMAGE_ERASE operation,
but instead manually clears the region. The render does the
corresponding thing.
---
 grid.c | 44 +++++++++++++++++++-------------------------
 main.c | 46 ++++++++++++++++++++++++++++++++--------------
 2 files changed, 51 insertions(+), 39 deletions(-)

diff --git a/grid.c b/grid.c
index f588f6e0..2663952d 100644
--- a/grid.c
+++ b/grid.c
@@ -164,26 +164,22 @@ grid_damage_scroll(struct grid *grid, enum damage_type damage_type,
 {
     damage_adjust_after_scroll(grid, damage_type, region, lines);
 
-    if (tll_length(grid->scroll_damage) > 0 &&
-        tll_back(grid->scroll_damage).type == damage_type &&
-        tll_back(grid->scroll_damage).scroll.region.start == region.start &&
-        tll_back(grid->scroll_damage).scroll.region.end == region.end)
-    {
-        /* Merge with existing scroll damage */
-
+    if (tll_length(grid->scroll_damage) > 0) {
         struct damage *dmg = &tll_back(grid->scroll_damage);
-        dmg->scroll.lines += lines;
 
-        /* If we've scrolled away the entire screen, remove it all together */
-        if (dmg->scroll.lines >= region.end - region.start)
-            tll_pop_back(grid->scroll_damage);
-    } else {
-        struct damage dmg = {
-            .type = damage_type,
-            .scroll = {.region = region, .lines = lines},
-        };
-        tll_push_back(grid->scroll_damage, dmg);
+        if (dmg->type == damage_type &&
+            dmg->scroll.region.start == region.start &&
+            dmg->scroll.region.end == region.end)
+        {
+            dmg->scroll.lines += lines;
+            return;
+        }
     }
+    struct damage dmg = {
+        .type = damage_type,
+        .scroll = {.region = region, .lines = lines},
+    };
+    tll_push_back(grid->scroll_damage, dmg);
 }
 
 void
@@ -277,11 +273,10 @@ grid_scroll_partial(struct grid *grid, struct scroll_region region, int rows)
         &grid->cells[cell_dst], &grid->cells[cell_src],
         bytes);
 
+    memset(&grid->cells[(region.end - rows) * grid->cols], 0,
+           rows * grid->cols * sizeof(grid->cells[0]));
+
     grid_damage_scroll(grid, DAMAGE_SCROLL, region, rows);
-    grid_erase(
-        grid,
-        (region.end - rows) * grid->cols,
-        region.end * grid->cols);
 }
 
 void
@@ -311,11 +306,10 @@ grid_scroll_reverse_partial(struct grid *grid,
         &grid->cells[cell_dst], &grid->cells[cell_src],
         bytes);
 
+    memset(&grid->cells[cell_src], 0,
+           rows * grid->cols * sizeof(grid->cells[0]));
+
     grid_damage_scroll(grid, DAMAGE_SCROLL_REVERSE, region, rows);
-    grid_erase(
-        grid,
-        region.start * grid->cols,
-        (region.start + rows) * grid->cols);
 }
 
 void
diff --git a/main.c b/main.c
index 296414b7..781db37b 100644
--- a/main.c
+++ b/main.c
@@ -27,6 +27,7 @@
 #include "grid.h"
 
 #define min(x, y) ((x) < (y) ? (x) : (y))
+#define max(x, y) ((x) > (y) ? (x) : (y))
 
 static const uint32_t default_foreground = 0xffffffff;
 static const uint32_t default_background = 0x000000ff;
@@ -269,25 +270,28 @@ grid_render_scroll(struct context *c, struct buffer *buf,
             dst_y, src_y, height, stride,
             buf->size);
 
-    cairo_surface_flush(buf->cairo_surface);
-    uint8_t *raw = cairo_image_surface_get_data(buf->cairo_surface);
+    if (height > 0) {
+        cairo_surface_flush(buf->cairo_surface);
+        uint8_t *raw = cairo_image_surface_get_data(buf->cairo_surface);
 
-    memmove(raw + dst_y * stride, raw + src_y * stride, height * stride);
-    cairo_surface_mark_dirty(buf->cairo_surface);
+        memmove(raw + dst_y * stride, raw + src_y * stride, height * stride);
+        cairo_surface_mark_dirty(buf->cairo_surface);
 
-    wl_surface_damage_buffer(c->wl.surface, 0, dst_y, width, height);
+        wl_surface_damage_buffer(c->wl.surface, 0, dst_y, width, height);
+    }
 
-#if 0
     const int cols = c->term.grid.cols;
+
     struct damage erase = {
         .type = DAMAGE_ERASE,
         .range = {
-            .start = (dmg->scroll.region.end - dmg->scroll.lines) * cols,
-            .length = dmg->scroll.lines * cols
+            .start = max(dmg->scroll.region.end - dmg->scroll.lines,
+                         dmg->scroll.region.start) * cols,
+            .length = min(dmg->scroll.region.end - dmg->scroll.region.start,
+                          dmg->scroll.lines) * cols,
         },
     };
     grid_render_erase(c, buf, &erase);
-#endif
 }
 
 static void
@@ -308,13 +312,27 @@ grid_render_scroll_reverse(struct context *c, struct buffer *buf,
             dst_y, src_y, height, stride,
             buf->size);
 
-    cairo_surface_flush(buf->cairo_surface);
-    uint8_t *raw = cairo_image_surface_get_data(buf->cairo_surface);
+    if (height > 0) {
+        cairo_surface_flush(buf->cairo_surface);
+        uint8_t *raw = cairo_image_surface_get_data(buf->cairo_surface);
 
-    memmove(raw + dst_y * stride, raw + src_y * stride, height * stride);
-    cairo_surface_mark_dirty(buf->cairo_surface);
+        memmove(raw + dst_y * stride, raw + src_y * stride, height * stride);
+        cairo_surface_mark_dirty(buf->cairo_surface);
 
-    wl_surface_damage_buffer(c->wl.surface, 0, dst_y, width, height);
+        wl_surface_damage_buffer(c->wl.surface, 0, dst_y, width, height);
+    }
+
+    const int cols = c->term.grid.cols;
+
+    struct damage erase = {
+        .type = DAMAGE_ERASE,
+        .range = {
+            .start = dmg->scroll.region.start * cols,
+            .length = min(dmg->scroll.region.end - dmg->scroll.region.start,
+                          dmg->scroll.lines) * cols,
+        },
+    };
+    grid_render_erase(c, buf, &erase);
 }
 
 static void