create draggable gain markers

src/app.zig

@@ -199,7 +199,7 @@ pub const Transform = struct {
     pub const GainChanges = std.BoundedArray(GainChange, max_gain_changes);
     pub const GainChange = struct {
         gain: f64,
-        sample: f64
+        sample: f64,
     };
 
     gain_changes: GainChanges = .{},
@@ -1026,6 +1026,35 @@ pub const Project = struct {
         }
     }
 
+    pub fn updateGainChange(self: *Project, index: usize, sample_index: f64) void {
+        const gain_change: *Transform.GainChange = &self.gain_changes.slice()[index];
+
+        if (index > 0) {
+            if (self.gain_changes.buffer[index - 1].sample + SampleList.Block.capacity > sample_index) {
+                return;
+            }
+        }
+
+        if (index < self.gain_changes.len - 1) {
+            if (sample_index > self.gain_changes.buffer[index + 1].sample - SampleList.Block.capacity) {
+                return;
+            }
+        }
+
+        const previous_sample_index = gain_change.sample;
+        gain_change.sample = sample_index;
+
+        const invalidated_range = RangeF64.init(
+            @min(previous_sample_index, sample_index),
+            @max(previous_sample_index, sample_index)
+        );
+
+        var view_iter = self.views.iterator();
+        while (view_iter.next()) |view| {
+            view.invalidated_transform_ranges.append(invalidated_range) catch continue;
+        }
+    }
+
     // ------------------- Serialization ------------------ //
 
     pub fn initFromFile(self: *Project, allocator: Allocator, f: std.fs.File) !void {
@@ -1755,6 +1784,7 @@ pub fn tick(self: *App) !void {
                 for (view.invalidated_transform_ranges.constSlice()) |range| {
                     const from_block: usize = @intFromFloat(@divFloor(range.lower, block_size));
                     const to_block: usize   = @intFromFloat(@divFloor(@min(range.upper, @as(f64, @floatFromInt(reference_len)) - 1), block_size));
+                    if (from_block > to_block) continue;
                     const block_count = to_block - from_block + 1;
 
                     try computed_samples.ensureTotalBlocks(from_block + block_count);

src/components/view_ruler.zig

@@ -400,7 +400,7 @@ pub fn show(ctx: Context, box: *UI.Box, graph_box: *UI.Box, view_id: Id, axis: U
             //     }
             // }
 
-            for (0.., project.gain_changes.slice()) |i, gain_change| {
+            for (0.., project.gain_changes.slice()) |i, *gain_change| {
                 const color = srcery.bright_orange;
 
                 const sample = gain_change.sample;
@@ -422,7 +422,7 @@ pub fn show(ctx: Context, box: *UI.Box, graph_box: *UI.Box, view_id: Id, axis: U
                     .float_rect = ruler.getGraphDrawContext().getRect(sample - clickable_width/2, clickable_width, 0, 1),
                     .float_relative_to = ruler.graph_box,
                     .parent = ruler.graph_box,
-                    .flags = &.{ .draw_hot, .draw_active, .clickable },
+                    .flags = &.{ .draw_hot, .draw_active, .clickable, .draggable },
                     .hot_cursor = .mouse_cursor_pointing_hand,
                 });
 
@@ -434,11 +434,26 @@ pub fn show(ctx: Context, box: *UI.Box, graph_box: *UI.Box, view_id: Id, axis: U
 
                     _ = ui.label("Gain: {d:.3}", .{ gain_change.gain });
                 }
+
+                const view_range = view.getGraphView(axis);
+                const mouse_range = switch (axis) {
+                    .X => RangeF64.init(0, ruler.graph_box.persistent.size.x),
+                    .Y => RangeF64.init(0, ruler.graph_box.persistent.size.y)
+                };
+                const mouse_position = switch (axis) {
+                    .X => signal.mouse.x - ruler.graph_box.persistent.position.x,
+                    .Y => signal.mouse.y - ruler.graph_box.persistent.position.y
+                };
+
+                if (signal.dragged() and i != 0) {
+                    project.updateGainChange(i, mouse_range.remapTo(view_range.*, mouse_position));
+                }
             }
         }
     }
 
     const signal = ui.signal(box);
+    const view_range = view.getGraphView(axis);
     const mouse_position = switch (axis) {
         .X => signal.relative_mouse.x,
         .Y => signal.relative_mouse.y
@@ -447,7 +462,6 @@ pub fn show(ctx: Context, box: *UI.Box, graph_box: *UI.Box, view_id: Id, axis: U
         .X => RangeF64.init(0, box.persistent.size.x),
         .Y => RangeF64.init(0, box.persistent.size.y)
     };
-    const view_range = view.getGraphView(axis);
 
     if (signal.hot and view_range.size() > 0) {
         const mouse_position_on_graph = mouse_range.remapTo(view_range.*, mouse_position);