renderer/opengl: some comments

src/renderer/OpenGL.zig

@@ -1438,6 +1438,7 @@ pub fn drawFrame(self: *OpenGL, surface: *apprt.Surface) !void {
     }
 }
 
+/// Draw the custom shaders.
 fn drawCustomPrograms(
     self: *OpenGL,
     custom_state: *custom.State,
@@ -1456,13 +1457,7 @@ fn drawCustomPrograms(
         // Bind our cell program state, buffers
         const bind = try program.bind();
         defer bind.unbind();
-
+        try bind.draw();
-        try gl.drawElementsInstanced(
-            gl.c.GL_TRIANGLES,
-            6,
-            gl.c.GL_UNSIGNED_BYTE,
-            1,
-        );
     }
 }
 

src/renderer/opengl/custom.zig

@@ -10,6 +10,7 @@ const log = std.log.scoped(.opengl_custom);
 const UNIFORM_INDEX: gl.c.GLuint = 0;
 const UNIFORM_BINDING: gl.c.GLuint = 0;
 
+/// Global uniforms for custom shaders.
 pub const Uniforms = extern struct {
     resolution: [3]f32 align(16) = .{ 0, 0, 0 },
     time: f32 align(4) = 1,
@@ -23,7 +24,13 @@ pub const Uniforms = extern struct {
     sample_rate: f32 align(4) = 1,
 };
 
-/// The state associated with custom shaders.
+/// The state associated with custom shaders. This should only be initialized
+/// if there is at least one custom shader.
+///
+/// To use this, the main terminal shader should render to the framebuffer
+/// specified by "fbo". The resulting "fb_texture" will contain the color
+/// attachment. This is then used as the iChannel0 input to the custom
+/// shader.
 pub const State = struct {
     /// The uniform data
     uniforms: Uniforms,
@@ -40,12 +47,14 @@ pub const State = struct {
 
     /// The last time the frame was drawn. This is used to update
     /// the time uniform.
-    last_frame_time: std.time.Instant,
+    first_frame_time: std.time.Instant,
 
     pub fn init(
         alloc: Allocator,
         srcs: []const [:0]const u8,
     ) !State {
+        if (srcs.len == 0) return error.OneCustomShaderRequired;
+
         // Create our programs
         var programs = std.ArrayList(Program).init(alloc);
         defer programs.deinit();
@@ -126,7 +135,7 @@ pub const State = struct {
             .vao = vao,
             .ebo = ebo,
             .fb_texture = fb_tex,
-            .last_frame_time = try std.time.Instant.now(),
+            .first_frame_time = try std.time.Instant.now(),
         };
     }
 
@@ -169,8 +178,8 @@ pub const State = struct {
     /// this.
     pub fn newFrame(self: *State) !void {
         // Update our frame time
-        const now = std.time.Instant.now() catch self.last_frame_time;
+        const now = std.time.Instant.now() catch self.first_frame_time;
-        const since_ns: f32 = @floatFromInt(now.since(self.last_frame_time));
+        const since_ns: f32 = @floatFromInt(now.since(self.first_frame_time));
         self.uniforms.time = since_ns / std.time.ns_per_s;
         self.uniforms.time_delta = since_ns / std.time.ns_per_s;
 
@@ -249,6 +258,8 @@ pub const Program = struct {
         self.program.destroy();
     }
 
+    /// Bind the program for use. This should be called so that draw can
+    /// be called.
     pub fn bind(self: *const Program) !Binding {
         const program = try self.program.use();
         errdefer program.unbind();
@@ -264,5 +275,15 @@ pub const Program = struct {
         pub fn unbind(self: Binding) void {
             self.program.unbind();
         }
+
+        pub fn draw(self: Binding) !void {
+            _ = self;
+            try gl.drawElementsInstanced(
+                gl.c.GL_TRIANGLES,
+                6,
+                gl.c.GL_UNSIGNED_BYTE,
+                1,
+            );
+        }
     };
 };

src/renderer/shaders/temp.f.glsl

@@ -1,28 +0,0 @@
-#version 430 core
-
-layout(binding = 0, std140) uniform Globals
-{
-    vec3 iResolution;
-    float iTime;
-    float iTimeDelta;
-    float iFrameRate;
-    int iFrame;
-    float iChannelTime[4];
-    vec3 iChannelResolution[4];
-    vec4 iMouse;
-    vec4 iDate;
-    float iSampleRate;
-} _89;
-
-layout(binding = 1) uniform sampler2D iChannel0;
-
-layout(location = 0) out vec4 _fragColor;
-
-void main() {
-    // red
-    _fragColor = vec4(_89.iSampleRate, 0.0, 0.0, 1.0);
-
-    // maze
-    //vec4 I = gl_FragCoord;
-    //_fragColor = vec4(3)*modf(I*.1,I)[int(length(I)*1e4)&1];
-}