Add fallback GLES2 renderer

Currently Alacritty only works on hardware which supports OpenGL 3.3 or
more, which can become problematic with older devices. This patch adds a
new GLES2 renderer, since it is much more widely supported, especially
on weaker hardware like phones or a Raspberry Pi.

While the GLES2 renderer is slower than the OpenGL 3.3+ version, it is
still significantly faster than software rendering. However because of
this performance difference it is only used when necessary and there
should be no difference for machines supporting OpenGL 3.3+.

The two renderers are largely independent and separated in the
`renderer/text/glsl3` and `renderer/text/gles2` modules. Separate
shaders are also required for text rendering. The rectangle rendering
for underlines and the visual bell works identically for both versions,
but does have some version-specific shader code.

Fixes #128.

Co-authored-by: Christian Duerr <contact@christianduerr.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/alacritty/src/renderer/rects.rs b/alacritty/src/renderer/rects.rs
index 3c74b10b..8c600b6b 100644
--- a/alacritty/src/renderer/rects.rs
+++ b/alacritty/src/renderer/rects.rs
@@ -12,7 +12,7 @@ use alacritty_terminal::term::SizeInfo;
 use crate::display::content::RenderableCell;
 use crate::gl;
 use crate::gl::types::*;
-use crate::renderer::shader::{ShaderError, ShaderProgram};
+use crate::renderer::shader::{ShaderError, ShaderProgram, ShaderVersion};
 use crate::renderer::{self, cstr};
 
 #[derive(Debug, Copy, Clone)]
@@ -252,10 +252,10 @@ pub struct RectRenderer {
 }
 
 impl RectRenderer {
-    pub fn new() -> Result<Self, renderer::Error> {
+    pub fn new(shader_version: ShaderVersion) -> Result<Self, renderer::Error> {
         let mut vao: GLuint = 0;
         let mut vbo: GLuint = 0;
-        let program = RectShaderProgram::new()?;
+        let program = RectShaderProgram::new(shader_version)?;
 
         unsafe {
             // Allocate buffers.
@@ -422,8 +422,8 @@ pub struct RectShaderProgram {
 }
 
 impl RectShaderProgram {
-    pub fn new() -> Result<Self, ShaderError> {
-        let program = ShaderProgram::new(RECT_SHADER_V, RECT_SHADER_F)?;
+    pub fn new(shader_version: ShaderVersion) -> Result<Self, ShaderError> {
+        let program = ShaderProgram::new(shader_version, RECT_SHADER_V, RECT_SHADER_F)?;
 
         Ok(Self {
             u_rect_kind: program.get_uniform_location(cstr!("rectKind"))?,