dynamically allocate quads as needed

This removes the pre-allocated (at resize) number of quads
and replaces it with a dynamic mechanism that tracks how many
quads are needed for a frame and then will re-allocate and
re-render when there weren't enough.

We start with 1024 quads and try to allocate in multiples
of 1024 quads.

refs: #986

wezterm-gui/src/renderstate.rs

@@ -22,10 +22,16 @@ pub struct MappedQuads<'a> {
 impl<'a> MappedQuads<'a> {
     pub fn allocate<'b>(&'b mut self) -> anyhow::Result<Quad<'b>> {
         let idx = *self.next;
-        if idx >= self.capacity {
-            anyhow::bail!("not enough quads! do something like OutOfTextureSpace");
-        }
         *self.next += 1;
+        let idx = if idx >= self.capacity {
+            // We don't have enough quads, so we'll keep re-using
+            // the first quad until we reach the end of the render
+            // pass, at which point we'll detect this condition
+            // and re-allocate the quads.
+            0
+        } else {
+            idx
+        };
 
         let idx = idx * VERTICES_PER_CELL;
         let mut quad = Quad {
@@ -52,6 +58,15 @@ impl TripleVertexBuffer {
         *self.next_quad.borrow_mut() = 0;
     }
 
+    pub fn need_more_quads(&self) -> Option<usize> {
+        let next = *self.next_quad.borrow();
+        if next > self.capacity {
+            Some(next)
+        } else {
+            None
+        }
+    }
+
     pub fn vertex_index_count(&self) -> (usize, usize) {
         let num_quads = *self.next_quad.borrow();
         (num_quads * VERTICES_PER_CELL, num_quads * INDICES_PER_CELL)
@@ -104,8 +119,6 @@ impl RenderState {
         fonts: &Rc<FontConfiguration>,
         metrics: &RenderMetrics,
         mut atlas_size: usize,
-        pixel_width: usize,
-        pixel_height: usize,
     ) -> anyhow::Result<Self> {
         loop {
             let glyph_cache =
@@ -123,12 +136,7 @@ impl RenderState {
                     // Last prog outputs srgb for gamma correction
                     let img_prog = Self::compile_prog(&context, true, Self::img_shader)?;
 
-                    let glyph_vertex_buffer = Self::compute_vertices(
-                        &context,
-                        metrics,
-                        pixel_width as f32,
-                        pixel_height as f32,
-                    )?;
+                    let glyph_vertex_buffer = Self::compute_vertices(&context, 1024)?;
 
                     return Ok(Self {
                         context,
@@ -183,18 +191,8 @@ impl RenderState {
         anyhow::bail!("Failed to compile shaders: {}", errors.join("\n"))
     }
 
-    pub fn advise_of_window_size_change(
-        &mut self,
-        metrics: &RenderMetrics,
-        pixel_width: usize,
-        pixel_height: usize,
-    ) -> anyhow::Result<()> {
-        let glyph_vertex_buffer = Self::compute_vertices(
-            &self.context,
-            metrics,
-            pixel_width as f32,
-            pixel_height as f32,
-        )?;
+    pub fn reallocate_quads(&mut self, num_quads: usize) -> anyhow::Result<()> {
+        let glyph_vertex_buffer = Self::compute_vertices(&self.context, num_quads)?;
 
         self.glyph_vertex_buffer = glyph_vertex_buffer;
         Ok(())
@@ -276,25 +274,8 @@ impl RenderState {
     /// let the GPU figure out the rest.
     fn compute_vertices(
         context: &Rc<GliumContext>,
-        metrics: &RenderMetrics,
-        width: f32,
-        height: f32,
+        num_quads: usize,
     ) -> anyhow::Result<TripleVertexBuffer> {
-        let cell_width = metrics.cell_size.width as f32;
-        let cell_height = metrics.cell_size.height as f32;
-
-        let num_cols = width as usize / cell_width as usize;
-        let num_rows = height as usize / cell_height as usize;
-
-        log::debug!(
-            "compute_vertices {}x{} {}x{}",
-            num_cols,
-            num_rows,
-            width,
-            height,
-        );
-
-        let num_quads = num_cols * num_rows + 2 /* bg image, scroll thumb */;
         let verts = vec![Vertex::default(); num_quads * VERTICES_PER_CELL];
         let mut indices = vec![];
         indices.reserve(num_quads * INDICES_PER_CELL);
@@ -319,7 +300,7 @@ impl RenderState {
                 VertexBuffer::dynamic(context, &verts)?,
                 VertexBuffer::dynamic(context, &verts)?,
             ]),
-            capacity: verts.len() / VERTICES_PER_CELL,
+            capacity: num_quads,
             indices: IndexBuffer::new(
                 context,
                 glium::index::PrimitiveType::TrianglesList,

wezterm-gui/src/termwindow/mod.rs

@@ -298,14 +298,7 @@ impl TermWindow {
     ) -> anyhow::Result<()> {
         self.render_state = None;
 
-        match RenderState::new(
-            ctx,
-            &self.fonts,
-            &self.render_metrics,
-            ATLAS_SIZE,
-            self.dimensions.pixel_width,
-            self.dimensions.pixel_height,
-        ) {
+        match RenderState::new(ctx, &self.fonts, &self.render_metrics, ATLAS_SIZE) {
             Ok(gl) => {
                 log::info!(
                     "OpenGL initialized! {} {} is_context_loss_possible={} wezterm version: {}",

wezterm-gui/src/termwindow/render.rs

@@ -99,7 +99,27 @@ impl super::TermWindow {
 
         for pass in 0.. {
             match self.paint_opengl_pass() {
-                Ok(_) => break,
+                Ok(_) => {
+                    let gl_state = self.render_state.as_mut().unwrap();
+                    if let Some(need_quads) = gl_state.glyph_vertex_buffer.need_more_quads() {
+                        // Round up to next multiple of 1024 that is >=
+                        // the number of needed quads for this frame
+                        let num_quads = (need_quads + 1023) & !1023;
+                        if let Err(err) = gl_state.reallocate_quads(num_quads) {
+                            log::error!(
+                                "Failed to allocate {} quads (needed {}): {:#}",
+                                num_quads,
+                                need_quads,
+                                err
+                            );
+                            break;
+                        }
+                        log::trace!("Allocated {} quads (needed {})", num_quads, need_quads);
+                        continue;
+                    }
+
+                    break;
+                }
                 Err(err) => {
                     if let Some(&OutOfTextureSpace {
                         size: Some(size),

wezterm-gui/src/termwindow/resize.rs

@@ -74,10 +74,8 @@ impl super::TermWindow {
     pub fn apply_dimensions(
         &mut self,
         dimensions: &Dimensions,
-        mut scale_changed_cells: Option<RowsAndCols>,
+        scale_changed_cells: Option<RowsAndCols>,
     ) {
-        let orig_dimensions = self.dimensions;
-
         self.dimensions = *dimensions;
 
         // Technically speaking, we should compute the rows and cols
@@ -143,25 +141,8 @@ impl super::TermWindow {
             (size, *dimensions)
         };
 
-        if let Some(render_state) = self.render_state.as_mut() {
-            if let Err(err) = render_state.advise_of_window_size_change(
-                &self.render_metrics,
-                dimensions.pixel_width,
-                dimensions.pixel_height,
-            ) {
-                log::error!(
-                    "failed to advise of resize from {:?} -> {:?}: {:?}",
-                    orig_dimensions,
-                    dimensions,
-                    err
-                );
-                // Try to restore the original dimensions
-                self.dimensions = orig_dimensions;
-                // Avoid the inner resize below
-                scale_changed_cells.take();
-            } else {
-                self.terminal_size = size;
-            }
+        if self.render_state.is_some() {
+            self.terminal_size = size;
         }
 
         let mux = Mux::get().unwrap();