Add Shader and Version

to simplify and constrain `program::create`

glow/src/program.rs

@@ -1,29 +1,118 @@
 use glow::HasContext;
 
+/// The [`Version`] of a `Program`.
+pub struct Version {
+    vertex: String,
+    fragment: String,
+}
+
+impl Version {
+    pub fn new(gl: &glow::Context) -> Version {
+        let version = gl.version();
+
+        let (vertex, fragment) = match (
+            version.major,
+            version.minor,
+            version.is_embedded,
+        ) {
+            // OpenGL 3.0+
+            (3, 0 | 1 | 2, false) => (
+                format!("#version 1{}0", version.minor + 3),
+                format!(
+                    "#version 1{}0\n#define HIGHER_THAN_300 1",
+                    version.minor + 3
+                ),
+            ),
+            // OpenGL 3.3+
+            (3 | 4, _, false) => (
+                format!("#version {}{}0", version.major, version.minor),
+                format!(
+                    "#version {}{}0\n#define HIGHER_THAN_300 1",
+                    version.major, version.minor
+                ),
+            ),
+            // OpenGL ES 3.0+
+            (3, _, true) => (
+                format!("#version 3{}0 es", version.minor),
+                format!(
+                    "#version 3{}0 es\n#define HIGHER_THAN_300 1",
+                    version.minor
+                ),
+            ),
+            // OpenGL ES 2.0+
+            (2, _, true) => (
+                String::from(
+                    "#version 100\n#define in attribute\n#define out varying",
+                ),
+                String::from("#version 100\n#define in varying"),
+            ),
+            // OpenGL 2.1
+            (2, _, false) => (
+                String::from(
+                    "#version 120\n#define in attribute\n#define out varying",
+                ),
+                String::from("#version 120\n#define in varying"),
+            ),
+            // OpenGL 1.1+
+            _ => panic!("Incompatible context version: {:?}", version),
+        };
+
+        log::info!("Shader directive: {}", vertex.lines().next().unwrap());
+
+        Version { vertex, fragment }
+    }
+}
+
+pub struct Shader(<glow::Context as HasContext>::Shader);
+
+impl Shader {
+    fn compile(gl: &glow::Context, stage: u32, content: &str) -> Shader {
+        unsafe {
+            let shader = gl.create_shader(stage).expect("Cannot create shader");
+
+            gl.shader_source(shader, &content);
+            gl.compile_shader(shader);
+
+            if !gl.get_shader_compile_status(shader) {
+                panic!("{}", gl.get_shader_info_log(shader));
+            }
+
+            Shader(shader)
+        }
+    }
+
+    /// Creates a vertex [`Shader`].
+    pub fn vertex(
+        gl: &glow::Context,
+        version: &Version,
+        content: &'static str,
+    ) -> Self {
+        let content = format!("{}\n{}", version.vertex, content);
+
+        Shader::compile(gl, glow::VERTEX_SHADER, &content)
+    }
+
+    /// Creates a fragment [`Shader`].
+    pub fn fragment(
+        gl: &glow::Context,
+        version: &Version,
+        content: &'static str,
+    ) -> Self {
+        let content = format!("{}\n{}", version.fragment, content);
+
+        Shader::compile(gl, glow::FRAGMENT_SHADER, &content)
+    }
+}
+
 pub unsafe fn create(
     gl: &glow::Context,
-    shader_sources: &[(u32, &str)],
+    shaders: &[Shader],
     attributes: &[(u32, &str)],
 ) -> <glow::Context as HasContext>::Program {
     let program = gl.create_program().expect("Cannot create program");
 
-    let mut shaders = Vec::with_capacity(shader_sources.len());
-
-    for (shader_type, shader_source) in shader_sources.iter() {
-        let shader = gl
-            .create_shader(*shader_type)
-            .expect("Cannot create shader");
-
-        gl.shader_source(shader, shader_source);
-        gl.compile_shader(shader);
-
-        if !gl.get_shader_compile_status(shader) {
-            panic!("{}", gl.get_shader_info_log(shader));
-        }
-
-        gl.attach_shader(program, shader);
-
-        shaders.push(shader);
+    for shader in shaders {
+        gl.attach_shader(program, shader.0);
     }
 
     for (i, name) in attributes {
@@ -36,8 +125,8 @@ pub unsafe fn create(
     }
 
     for shader in shaders {
-        gl.detach_shader(program, shader);
-        gl.delete_shader(shader);
+        gl.detach_shader(program, shader.0);
+        gl.delete_shader(shader.0);
     }
 
     program