Fix incorrect padding calculations

The extra window padding was calculated in the renderer which lead to
problems with the paddings calculated in the `src/display.rs` and
`src/term/mod.rs`.

As a solution, every instance of `config.padding().x/y` has been removed
from the renderer (`src/renderer/mod.rs`), instead the padding is always
passed through from the `src/display.rs`.

The initial calculations during display creation and after resize then
are scaled appropriately and then the extra padding is calculated. As a
result every other location can just make use of the correctly
calculated `size_info.padding_x` and `size_info.padding_y`.

The documentation has been changed to clearly state that the padding is
scaled by DPI now.

This fixes #1773.

2 files changed, 50 insertions, 57 deletions

diff --git a/src/display.rs b/src/display.rs
index 5fbaf44a..e170c152 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -144,28 +144,34 @@ impl Display {
             .expect("glutin returns window size").to_physical(dpr);
 
         // Create renderer
-        let mut renderer = QuadRenderer::new(config, viewport_size, dpr)?;
+        let mut renderer = QuadRenderer::new(viewport_size)?;
 
         let (glyph_cache, cell_width, cell_height) =
             Self::new_glyph_cache(dpr, &mut renderer, config)?;
 
-
         let dimensions = options.dimensions()
             .unwrap_or_else(|| config.dimensions());
 
-        // Resize window to specified dimensions unless one or both dimensions are 0
-        if dimensions.columns_u32() > 0 && dimensions.lines_u32() > 0 {
-            let width = cell_width as u32 * dimensions.columns_u32();
-            let height = cell_height as u32 * dimensions.lines_u32();
+        debug_assert!(dimensions.columns_u32() > 0);
+        debug_assert!(dimensions.lines_u32() > 0);
 
-            let new_viewport_size = PhysicalSize::new(
-                f64::from(width + 2 * (f64::from(config.padding().x) * dpr) as u32),
-                f64::from(height + 2 * (f64::from(config.padding().y) * dpr) as u32) as f64);
+        let width = cell_width as u32 * dimensions.columns_u32();
+        let height = cell_height as u32 * dimensions.lines_u32();
 
-            window.set_inner_size(new_viewport_size.to_logical(dpr));
-            renderer.resize(new_viewport_size, dpr, cell_width as i32, cell_height as i32);
-            viewport_size = new_viewport_size;
-        }
+        let mut padding_x = f64::from(config.padding().x) * dpr;
+        let mut padding_y = f64::from(config.padding().y) * dpr;
+        padding_x = padding_x + (f64::from(width) - 2. * padding_x) % f64::from(cell_width) / 2.;
+        padding_y = padding_y + (f64::from(height) - 2. * padding_y) % f64::from(cell_height) / 2.;
+        padding_x = padding_x.floor();
+        padding_y = padding_y.floor();
+
+        viewport_size = PhysicalSize::new(
+            f64::from(width) + 2. * padding_x,
+            f64::from(height) + 2. * padding_y,
+        );
+
+        window.set_inner_size(viewport_size.to_logical(dpr));
+        renderer.resize(viewport_size, padding_x as f32, padding_y as f32);
 
         info!("Cell Size: ({} x {})", cell_width, cell_height);
 
@@ -175,8 +181,8 @@ impl Display {
             height: viewport_size.height as f32,
             cell_width: cell_width as f32,
             cell_height: cell_height as f32,
-            padding_x: (f64::from(config.padding().x) * dpr).floor() as f32,
-            padding_y: (f64::from(config.padding().y) * dpr).floor() as f32,
+            padding_x: padding_x as f32,
+            padding_y: padding_y as f32,
         };
 
         // Channel for resize events
@@ -302,16 +308,27 @@ impl Display {
 
             self.font_size = terminal.font_size;
             self.size_info.dpr = dpr;
-            self.size_info.padding_x = (f64::from(config.padding().x) * dpr).floor() as f32;
-            self.size_info.padding_y = (f64::from(config.padding().y) * dpr).floor() as f32;
+
             self.update_glyph_cache(config);
         }
 
         // Receive any resize events; only call gl::Viewport on last
         // available
         if let Some(psize) = new_size.take() {
-            self.size_info.width = psize.width as f32;
-            self.size_info.height = psize.height as f32;
+            let width = psize.width as f32;
+            let height = psize.height as f32;
+            let cell_width = self.size_info.cell_width;
+            let cell_height = self.size_info.cell_height;
+
+            self.size_info.width = width;
+            self.size_info.height = height;
+
+            let mut padding_x = f32::from(config.padding().x) * dpr as f32;
+            let mut padding_y = f32::from(config.padding().y) * dpr as f32;
+            padding_x = (padding_x + ((width - 2. * padding_x) % cell_width) / 2.).floor();
+            padding_y = (padding_y + ((height - 2. * padding_y) % cell_height) / 2.).floor();
+            self.size_info.padding_x = padding_x;
+            self.size_info.padding_y = padding_y;
 
             let size = &self.size_info;
             terminal.resize(size);
@@ -320,11 +337,8 @@ impl Display {
                 item.on_resize(size)
             }
 
-            let cw = self.size_info.cell_width as i32;
-            let ch = self.size_info.cell_height as i32;
-
             self.window.resize(psize);
-            self.renderer.resize(psize, dpr, cw, ch);
+            self.renderer.resize(psize, padding_x, padding_y);
         }
     }
 
diff --git a/src/renderer/mod.rs b/src/renderer/mod.rs
index 8e0fc60b..1a193caf 100644
--- a/src/renderer/mod.rs
+++ b/src/renderer/mod.rs
@@ -118,9 +118,6 @@ pub struct ShaderProgram {
     ///
     /// Rendering is split into two passes; 1 for backgrounds, and one for text
     u_background: GLint,
-
-    padding_x: u8,
-    padding_y: u8,
 }
 
 #[derive(Debug, Clone)]
@@ -472,8 +469,8 @@ const ATLAS_SIZE: i32 = 1024;
 
 impl QuadRenderer {
     // TODO should probably hand this a transform instead of width/height
-    pub fn new(config: &Config, size: PhysicalSize, dpr: f64) -> Result<QuadRenderer, Error> {
-        let program = ShaderProgram::new(config, size, dpr)?;
+    pub fn new(size: PhysicalSize) -> Result<QuadRenderer, Error> {
+        let program = ShaderProgram::new(size)?;
 
         let mut vao: GLuint = 0;
         let mut vbo: GLuint = 0;
@@ -668,7 +665,7 @@ impl QuadRenderer {
         while let Ok(msg) = self.rx.try_recv() {
             match msg {
                 Msg::ShaderReload => {
-                    self.reload_shaders(config, PhysicalSize::new(f64::from(props.width), f64::from(props.height)), props.dpr);
+                    self.reload_shaders(PhysicalSize::new(f64::from(props.width), f64::from(props.height)));
                 }
             }
         }
@@ -720,9 +717,9 @@ impl QuadRenderer {
         })
     }
 
-    pub fn reload_shaders(&mut self, config: &Config, size: PhysicalSize, dpr: f64) {
+    pub fn reload_shaders(&mut self, size: PhysicalSize) {
         warn!("Reloading shaders ...");
-        let program = match ShaderProgram::new(config, size, dpr) {
+        let program = match ShaderProgram::new(size) {
             Ok(program) => {
                 warn!(" ... OK");
                 program
@@ -748,30 +745,21 @@ impl QuadRenderer {
         self.program = program;
     }
 
-    pub fn resize(&mut self, size: PhysicalSize, dpr: f64, cell_width: i32, cell_height: i32) {
+    pub fn resize(&mut self, size: PhysicalSize, padding_x: f32, padding_y: f32) {
         let (width, height): (u32, u32) = size.into();
-        let (width, height) = (width as i32, height as i32);
-
-        let mut padding_x = (f64::from(self.program.padding_x) * dpr) as i32;
-        let mut padding_y = (f64::from(self.program.padding_y) * dpr) as i32;
-
-        // Add padding to center the grid inside the window
-        padding_y += ((height - 2 * padding_y) % cell_height) / 2;
-        padding_x += ((width - 2 * padding_x) % cell_width) / 2;
 
         // viewport
         unsafe {
+            let width = width as i32;
+            let height = height as i32;
+            let padding_x = padding_x as i32;
+            let padding_y = padding_y as i32;
             gl::Viewport(padding_x, padding_y, width - 2 * padding_x, height - 2 * padding_y);
         }
 
         // update projection
         self.program.activate();
-        self.program.update_projection(
-            width as f32,
-            height as f32,
-            padding_x as f32,
-            padding_y as f32,
-        );
+        self.program.update_projection(width as f32, height as f32, padding_x, padding_y);
         self.program.deactivate();
     }
 }
@@ -1007,11 +995,7 @@ impl ShaderProgram {
         }
     }
 
-    pub fn new(
-        config: &Config,
-        size: PhysicalSize,
-        dpr: f64
-    ) -> Result<ShaderProgram, ShaderCreationError> {
+    pub fn new(size: PhysicalSize) -> Result<ShaderProgram, ShaderCreationError> {
         let vertex_source = if cfg!(feature = "live-shader-reload") {
             None
         } else {
@@ -1061,9 +1045,6 @@ impl ShaderProgram {
 
         assert_uniform_valid!(projection, term_dim, cell_dim);
 
-        let padding_x = (f32::from(config.padding().x) * dpr as f32).floor();
-        let padding_y = (f32::from(config.padding().y) * dpr as f32).floor();
-
         let shader = ShaderProgram {
             id: program,
             u_projection: projection,
@@ -1071,11 +1052,9 @@ impl ShaderProgram {
             u_cell_dim: cell_dim,
             u_visual_bell: visual_bell,
             u_background: background,
-            padding_x: padding_x as u8,
-            padding_y: padding_y as u8,
         };
 
-        shader.update_projection(size.width as f32, size.height as f32, padding_x, padding_y);
+        shader.update_projection(size.width as f32, size.height as f32, 0., 0.);
 
         shader.deactivate();