Merge pull request #2497 from stefanhaller/fix-initial-scroll-bar-size

3 files changed, 32 insertions, 8 deletions

diff --git a/pkg/gui/pty.go b/pkg/gui/pty.go
index 4a87c98da..fe53697c8 100644
--- a/pkg/gui/pty.go
+++ b/pkg/gui/pty.go
@@ -55,9 +55,6 @@ func (gui *Gui) newPtyTask(view *gocui.View, cmd *exec.Cmd, prefix string) error
 
 	cmd.Env = append(cmd.Env, "GIT_PAGER="+pager)
 
-	_, height := view.Size()
-	_, oy := view.Origin()
-
 	manager := gui.getManager(view)
 
 	var ptmx *os.File
@@ -82,7 +79,8 @@ func (gui *Gui) newPtyTask(view *gocui.View, cmd *exec.Cmd, prefix string) error
 		gui.Mutexes.PtyMutex.Unlock()
 	}
 
-	if err := manager.NewTask(manager.NewCmdTask(start, prefix, height+oy+10, onClose), cmdStr); err != nil {
+	linesToRead := gui.linesToReadFromCmdTask(view)
+	if err := manager.NewTask(manager.NewCmdTask(start, prefix, linesToRead, onClose), cmdStr); err != nil {
 		return err
 	}
 
diff --git a/pkg/gui/tasks_adapter.go b/pkg/gui/tasks_adapter.go
index 33aa09eb9..69b64d7b1 100644
--- a/pkg/gui/tasks_adapter.go
+++ b/pkg/gui/tasks_adapter.go
@@ -16,9 +16,6 @@ func (gui *Gui) newCmdTask(view *gocui.View, cmd *exec.Cmd, prefix string) error
 		cmdStr,
 	).Debug("RunCommand")
 
-	_, height := view.Size()
-	_, oy := view.Origin()
-
 	manager := gui.getManager(view)
 
 	start := func() (*exec.Cmd, io.Reader) {
@@ -35,7 +32,8 @@ func (gui *Gui) newCmdTask(view *gocui.View, cmd *exec.Cmd, prefix string) error
 		return cmd, r
 	}
 
-	if err := manager.NewTask(manager.NewCmdTask(start, prefix, height+oy+10, nil), cmdStr); err != nil {
+	linesToRead := gui.linesToReadFromCmdTask(view)
+	if err := manager.NewTask(manager.NewCmdTask(start, prefix, linesToRead, nil), cmdStr); err != nil {
 		gui.c.Log.Error(err)
 	}
 
diff --git a/pkg/gui/view_helpers.go b/pkg/gui/view_helpers.go
index c51942b03..8f2055245 100644
--- a/pkg/gui/view_helpers.go
+++ b/pkg/gui/view_helpers.go
@@ -6,6 +6,7 @@ import (
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/gui/keybindings"
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
+	"github.com/jesseduffield/lazygit/pkg/tasks"
 	"github.com/jesseduffield/lazygit/pkg/utils"
 	"github.com/spkg/bom"
 )
@@ -15,6 +16,33 @@ func (gui *Gui) resetOrigin(v *gocui.View) error {
 	return v.SetOrigin(0, 0)
 }
 
+// Returns the number of lines that we should read initially from a cmd task so
+// that the scrollbar has the correct size, along with the number of lines after
+// which the view is filled and we can do a first refresh.
+func (gui *Gui) linesToReadFromCmdTask(v *gocui.View) tasks.LinesToRead {
+	_, height := v.Size()
+	_, oy := v.Origin()
+
+	linesForFirstRefresh := height + oy + 10
+
+	// We want to read as many lines initially as necessary to let the
+	// scrollbar go to its minimum height, so that the scrollbar thumb doesn't
+	// change size as you scroll down.
+	minScrollbarHeight := 2
+	linesToReadForAccurateScrollbar := height*(height-1)/minScrollbarHeight + oy
+
+	// However, cap it at some arbitrary max limit, so that we don't get
+	// performance problems for huge monitors or tiny font sizes
+	if linesToReadForAccurateScrollbar > 5000 {
+		linesToReadForAccurateScrollbar = 5000
+	}
+
+	return tasks.LinesToRead{
+		Total:               linesToReadForAccurateScrollbar,
+		InitialRefreshAfter: linesForFirstRefresh,
+	}
+}
+
 func (gui *Gui) cleanString(s string) string {
 	output := string(bom.Clean([]byte(s)))
 	return utils.NormalizeLinefeeds(output)