From 4d9b67fa65f2e8235f7206c332239271b93a7f17 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 15 Apr 2022 09:10:32 -0700
Subject: [PATCH] model direct gpu cell

---
 shaders/cell.v.glsl   |  9 +--------
 src/Grid.zig          | 41 ++++++++++++++++++++++++++++-------------
 src/opengl/Buffer.zig | 16 ++++++++--------
 3 files changed, 37 insertions(+), 29 deletions(-)

diff --git a/shaders/cell.v.glsl b/shaders/cell.v.glsl
index aaa03d78e..e1fa65c68 100644
--- a/shaders/cell.v.glsl
+++ b/shaders/cell.v.glsl
@@ -12,13 +12,6 @@ flat out vec4 bg_color;
 uniform vec2 cell_size;
 uniform mat4 projection;
 
-vec3 hsv2rgb(vec3 c)
-{
-    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
-    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
-    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
-}
-
 void main() {
     // Top-left cell coordinates converted to world space
     vec2 cell_pos = cell_size * grid_coord;
@@ -34,5 +27,5 @@ void main() {
     cell_pos = cell_pos + cell_size * position;
 
     gl_Position = projection * vec4(cell_pos, 1.0, 1.0);
-    bg_color = vec4(hsv2rgb(bg_color_in.rgb), 1.0);
+    bg_color = vec4(bg_color_in.rgb / 255.0, 1.0);
 }
diff --git a/src/Grid.zig b/src/Grid.zig
index d816231d2..fe15f85bc 100644
--- a/src/Grid.zig
+++ b/src/Grid.zig
@@ -26,6 +26,19 @@ vao: gl.VertexArray,
 ebo: gl.Buffer,
 vbo: gl.Buffer,
 
+/// The raw structure that maps directly to the buffer sent to the vertex shader.
+const GPUCell = struct {
+    /// vec2 grid_coord
+    grid_col: u16,
+    grid_row: u16,
+
+    /// vec4 bg_color_in
+    bg_r: u8,
+    bg_g: u8,
+    bg_b: u8,
+    bg_a: u8,
+};
+
 pub fn init(alloc: Allocator) !Grid {
     // Initialize our font atlas. We will initially populate the
     // font atlas with all the visible ASCII characters since they are common.
@@ -98,8 +111,13 @@ pub fn init(alloc: Allocator) !Grid {
     var vbobind = try vbo.bind(.ArrayBuffer);
     defer vbobind.unbind();
     //try vbobind.setDataNull(vertices.items, .StaticDraw);
-    try vbobind.attribute(0, 2, [6]f32, 0);
-    try vbobind.attribute(1, 4, [6]f32, 2);
+
+    var offset: usize = 0;
+    try vbobind.attributeAdvanced(0, 2, gl.c.GL_UNSIGNED_SHORT, false, @sizeOf(GPUCell), offset);
+    offset += 2 * @sizeOf(u16);
+    try vbobind.attributeAdvanced(1, 4, gl.c.GL_UNSIGNED_BYTE, false, @sizeOf(GPUCell), offset);
+    try vbobind.enableAttribArray(0);
+    try vbobind.enableAttribArray(1);
     try vbobind.attributeDivisor(0, 1);
     try vbobind.attributeDivisor(1, 1);
 
@@ -155,23 +173,20 @@ pub fn render(self: Grid) !void {
     defer gl.VertexArray.unbind() catch null;
 
     // Build our data
-    var vertices: std.ArrayListUnmanaged([6]f32) = .{};
+    var vertices: std.ArrayListUnmanaged(GPUCell) = .{};
     try vertices.ensureUnusedCapacity(self.alloc, self.size.columns * self.size.rows);
     defer vertices.deinit(self.alloc);
     var row: u32 = 0;
     while (row < self.size.rows) : (row += 1) {
         var col: u32 = 0;
         while (col < self.size.columns) : (col += 1) {
-            const rowf = @intToFloat(f32, row);
-            const colf = @intToFloat(f32, col);
-            const hue = ((colf * @intToFloat(f32, self.size.rows)) + rowf) / @intToFloat(f32, self.size.columns * self.size.rows);
-            vertices.appendAssumeCapacity([6]f32{
-                colf,
-                rowf,
-                hue,
-                0.7,
-                0.8,
-                1.0,
+            vertices.appendAssumeCapacity(.{
+                .grid_col = @intCast(u16, col),
+                .grid_row = @intCast(u16, row),
+                .bg_r = 200,
+                .bg_g = 100,
+                .bg_b = 150,
+                .bg_a = 255,
             });
         }
     }
diff --git a/src/opengl/Buffer.zig b/src/opengl/Buffer.zig
index d5fffac62..7fa3a41f9 100644
--- a/src/opengl/Buffer.zig
+++ b/src/opengl/Buffer.zig
@@ -134,18 +134,13 @@ pub const Binding = struct {
             else => @compileError("unsupported type"),
         };
 
-        const offsetPtr = if (offset > 0)
-            @intToPtr(*const anyopaque, offset * info.offset)
-        else
-            null;
-
         try b.attributeAdvanced(
             idx,
             size,
             info.typ,
             false,
             info.stride,
-            offsetPtr,
+            offset * info.offset,
         );
         try b.enableAttribArray(idx);
     }
@@ -163,10 +158,15 @@ pub const Binding = struct {
         typ: c.GLenum,
         normalized: bool,
         stride: c.GLsizei,
-        ptr: ?*const anyopaque,
+        offset: usize,
     ) !void {
         const normalized_c: c.GLboolean = if (normalized) c.GL_TRUE else c.GL_FALSE;
-        c.glVertexAttribPointer(idx, size, typ, normalized_c, stride, ptr);
+        const offsetPtr = if (offset > 0)
+            @intToPtr(*const anyopaque, offset)
+        else
+            null;
+
+        c.glVertexAttribPointer(idx, size, typ, normalized_c, stride, offsetPtr);
         try errors.getError();
     }