Allow switching out the default shaders

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mini_gl_fb"
-version = "0.1.1"
+version = "0.2.0"
 authors = ["shivshank"]
 
 [dependencies]

examples/custom_shaders.rs

@@ -0,0 +1,123 @@
+extern crate mini_gl_fb;
+
+/// Geometry shaders allow you to procedurally generate new geometry from the vertex data.
+///
+/// This shader takes the two triangles submitted by mini_gl_fb and turns them into a circle!
+const geometry_source: &str = r"
+    #version 330 core
+
+    layout (triangles) in;
+    layout (triangle_strip, max_vertices = 8) out;
+
+    in vec2 v_uv[];
+
+    out vec2 g_uv;
+
+    vec2 midpoint(vec2 a, vec2 b) {
+        return (a + b) / 2.0;
+    }
+
+    void main() {
+        // n.b., the way we do this relies almost entirely on what we know about the internals of
+        // mini_gl_fb, so you will need to refer to the source if you want to play with this stuff.
+
+        vec4 center = vec4(0.0, 0.0, 0.0, 1.0);
+        // for the first triangle, the second (index 1) vertex is the top left
+        // for the second triangle, it is the bottom right. we will treat that like a direction!
+        vec2 dir = gl_in[1].gl_Position.xy;
+
+        // we are turning each triangle into 4 triangles, which we output in triangle strips
+        // (remember this shader will get run twice, once for each input triangle)
+
+        vec4 top_left = vec4(normalize(vec2(dir.x, -dir.y)), 0.0, 1.0);
+        vec4 left = vec4(sign(dir.x), 0.0, 0.0, 1.0);
+        vec4 bottom_left = vec4(normalize(dir), 0.0, 1.0);
+        vec4 bottom = vec4(0.0, sign(dir.y), 0.0, 1.0);
+        vec4 bottom_right = vec4(normalize(vec2(-dir.x, dir.y)), 0.0, 1.0);
+
+        gl_Position = top_left;
+        g_uv = v_uv[0];
+        EmitVertex();
+
+        gl_Position = left;
+        g_uv = midpoint(v_uv[0], v_uv[1]);
+        EmitVertex();
+
+        gl_Position = center;
+        g_uv = midpoint(v_uv[0], v_uv[2]);
+        EmitVertex();
+
+        gl_Position = bottom_left;
+        g_uv = v_uv[1];
+        EmitVertex();
+
+        EndPrimitive();
+
+        gl_Position = bottom_left;
+        g_uv = v_uv[1];
+        EmitVertex();
+
+        gl_Position = bottom;
+        g_uv = midpoint(v_uv[1], v_uv[2]);
+        EmitVertex();
+
+        gl_Position = center;
+        g_uv = midpoint(v_uv[0], v_uv[2]);
+        EmitVertex();
+
+        gl_Position = bottom_right;
+        g_uv = v_uv[2];
+        EmitVertex();
+
+        EndPrimitive();
+    }
+";
+
+const fragment_source: &str = r"
+    #version 330 core
+
+    in vec2 g_uv;
+
+    out vec4 frag_color;
+
+    // this is the texture uploaded by calls to `update_buffer`
+    uniform sampler2D u_tex0;
+
+    void main() {
+        vec4 sample = texture(u_tex0, g_uv);
+        vec4 color;
+        if (sample.r == 1.0) {
+            color = sample;
+        } else {
+            // render the uv coords as color otherwise
+            color = vec4(g_uv, 0.0, 1.0);
+        }
+        frag_color = color;
+    }
+";
+
+extern crate gl;
+
+fn main() {
+    let width = 800;
+    let height = 600;
+
+    let mut fb = mini_gl_fb::gotta_go_fast("Hello shaders!", width, height);
+
+    let mut buffer = vec![[128u8, 0, 0, 255]; (width * height) as usize];
+    // let's write a red line into the buffer roughly along the diagonal (misses many pixels)
+    for i in 0..100 {
+        let j = i as f32 / 100.0;
+        let index = ((width as f32) * j * ((height as f32) + 1.0)).floor() as usize;
+        buffer[index] = [255, 0, 0, 255];
+    }
+
+    // Let's keep using the default vertex shader
+    // fb.use_vertex_shader(...);
+    fb.use_geometry_shader(geometry_source);
+    fb.use_fragment_shader(fragment_source);
+
+    fb.update_buffer(&buffer);
+
+    fb.persist_and_redraw(true);
+}

src/default_vertex_shader.glsl

@@ -1,7 +1,7 @@
 #version 330 core
 
-layout(location = 0) in ivec2 pos;
-layout(location = 1) in ivec2 uv;
+layout(location = 0) in vec2 pos;
+layout(location = 1) in vec2 uv;
 
 out vec2 v_uv;
 

src/lib.rs

@@ -13,7 +13,7 @@ use gl::types::*;
 
 use std::ptr::null;
 
-type VertexFormat = buffer_layout!([i8; 2], [u8; 2]);
+type VertexFormat = buffer_layout!([f32; 2], [f32; 2]);
 
 pub fn gotta_go_fast<S: ToString>(window_title: S, window_width: i32, window_height: i32) -> Framebuffer {
     let events_loop = glutin::EventsLoop::new();
@@ -61,15 +61,17 @@ pub fn gotta_go_fast<S: ToString>(window_title: S, window_width: i32, window_hei
         gl::BindVertexArray(vao);
         gl::BindBuffer(gl::ARRAY_BUFFER, vbo);
         VertexFormat::declare(0);
-        let verts = [
-            [-1i8, 1], [0, 0],
-            [-1, -1], [0, 1],
-            [1, -1], [1, 1],
-            [1, -1], [1, 1],
-            [1, 1], [1, 0],
-            [-1, 1], [0, 0],
+
+        let verts: [[f32; 2]; 12] = [
+            [-1., 1.], [0., 0.], // top left
+            [-1., -1.], [0., 1.], // bottom left
+            [1., -1.], [1., 1.], // bottom right
+            [1., -1.], [1., 1.], // bottom right
+            [1., 1.], [1., 0.], // top right
+            [-1., 1.], [0., 0.], // top left
         ];
-        gl::BufferData(gl::ARRAY_BUFFER, (verts.len() * 2) as _, verts.as_ptr() as *const _, gl::STATIC_DRAW);
+        use std::mem::size_of_val;
+        gl::BufferData(gl::ARRAY_BUFFER, size_of_val(&verts) as _, verts.as_ptr() as *const _, gl::STATIC_DRAW);
         gl::BindBuffer(gl::ARRAY_BUFFER, 0);
         gl::BindVertexArray(0);
     }
@@ -128,6 +130,21 @@ impl Framebuffer {
         })
     }
 
+    pub fn use_vertex_shader(&mut self, source: &str) {
+        rebuild_shader(&mut self.vertex_shader, gl::VERTEX_SHADER, source);
+        self.relink_program();
+    }
+
+    pub fn use_fragment_shader(&mut self, source: &str) {
+        rebuild_shader(&mut self.fragment_shader, gl::FRAGMENT_SHADER, source);
+        self.relink_program();
+    }
+
+    pub fn use_geometry_shader(&mut self, source: &str) {
+        rebuild_shader(&mut self.geometry_shader, gl::GEOMETRY_SHADER, source);
+        self.relink_program();
+    }
+
     pub fn change_buffer_format<T: ToGlType>(&mut self, format: BufferFormat) {
         self.texture_format = (format, T::to_gl_enum());
     }
@@ -173,6 +190,17 @@ impl Framebuffer {
             self.gl_window.swap_buffers().unwrap();
         }
     }
+
+    fn relink_program(&mut self) {
+        unsafe {
+            gl::DeleteProgram(self.program);
+            self.program = build_program(&[
+                self.vertex_shader,
+                self.fragment_shader,
+                self.geometry_shader,
+            ]);
+        }
+    }
 }
 
 #[derive(Copy, Clone, PartialEq, Eq)]
@@ -250,6 +278,30 @@ fn create_gl_buffer() -> Option<GLuint> {
     }
 }
 
+fn rebuild_shader(shader: &mut Option<GLuint>, kind: GLenum, source: &str) {
+    if let Some(shader) = *shader {
+        unsafe {
+            gl::DeleteShader(shader);
+        }
+    }
+    let compilation_result = rustic_gl::raw::create_shader(kind, source);
+    match compilation_result {
+        Ok(gl_id) => {
+            *shader = Some(gl_id);
+        },
+        Err(rustic_gl::error::GlError::ShaderCompilation(info)) => {
+            if let Some(log) = info {
+                panic!("Shader compilation failed with the following information: {}", log);
+            } else {
+                panic!("Shader compilation failed without any information.")
+            }
+        },
+        Err(err) => {
+            panic!("An error occured while compiling shader: {}", err);
+        }
+    }
+}
+
 unsafe fn build_program(shaders: &[Option<GLuint>]) -> GLuint {
     let program = rustic_gl::raw::create_program()
         .unwrap();