Line drawing optimizations, vertex indexing

src/Renderer.zig

@@ -104,10 +104,31 @@ pub fn setColor(self: *Self, r: u8, g: i32, b: i32, a: i32) void {
 }
 
 pub fn drawRectangle(self: *Self, x: i32, y: i32, w: i32, h: i32) void {
-    self.fillRectangle(x, y, 1, h);
-    self.fillRectangle(x, y, w, 1);
-    self.fillRectangle(w+x-1, y, 1, h);
-    self.fillRectangle(x, h+y-1, w, 1);
+    var xf = @intToFloat(f32, x);
+    var yf = @intToFloat(f32, y);
+    var wf = @intToFloat(f32, w);
+    var hf = @intToFloat(f32, h);
+
+    gl.enableVertexAttribArray(0);
+    gl.vertexAttribPointer(0, 2, .float, false, 0, 0);
+
+    const vertex_buffer = [_]f32{
+        xf,      yf     ,
+        xf + wf, yf     ,
+        xf + wf, yf + hf,
+        xf,      yf + hf,
+    };
+
+    const indices = [_]u8{0, 1, 1, 2, 2, 3, 3, 0};
+
+    self.buffer.data(f32, &vertex_buffer, .static_draw);
+
+    gl.uniform4fv(self.color_loc, &.{ self.color });
+    _ = indices;
+
+    gl.drawElements(.lines, 8, .u8, @ptrToInt(&indices));
+
+    gl.disableVertexAttribArray(0);
 }
 
 pub fn fillRectangle(self: *Self, x: i32, y: i32, w: i32, h: i32) void {
@@ -117,22 +138,22 @@ pub fn fillRectangle(self: *Self, x: i32, y: i32, w: i32, h: i32) void {
     var hf = @intToFloat(f32, h);
 
     gl.enableVertexAttribArray(0);
-    gl.vertexAttribPointer(0, 3, .float, false, 0, 0);
+    gl.vertexAttribPointer(0, 2, .float, false, 0, 0);
 
     const vertex_buffer = [_]f32{
-        xf,      yf     , 0.0,
-        xf + wf, yf     , 0.0,
-        xf,      yf + hf, 0.0,
-        xf + wf, yf + hf, 0.0,
-        xf + wf, yf     , 0.0,
-        xf,      yf + hf, 0.0,
+        xf + wf, yf     ,
+        xf,      yf + hf,
+        xf,      yf     ,
+        xf + wf, yf + hf,
     };
 
+    const indices = [_]u8{0, 1, 2, 0, 1, 3};
+
     self.buffer.data(f32, &vertex_buffer, .static_draw);
 
     gl.uniform4fv(self.color_loc, &.{ self.color });
-    gl.drawArrays(.triangles, 0, 3);
-    gl.drawArrays(.triangles, 3, 6);
+
+    gl.drawElements(.triangles, 6, .u8, @ptrToInt(&indices));
 
     gl.disableVertexAttribArray(0);
 }

src/main.zig

@@ -30,7 +30,15 @@ pub fn main() !void {
             .main_menu => main_menu.tick(),
             .game => game.tick(),
         };
+        const start = SDL.getTicks64();
+
 
         renderer.render();
+
+        const delay = SDL.getTicks64() - start;
+        std.debug.print("{} ms\n", .{delay});
+        if (delay < 16) {
+            SDL.delay(16 - @intCast(u32, delay));
+        }
     }
 }

src/shaders/vector.vs

@@ -1,8 +1,8 @@
 #version 330 core
 
 uniform mat4 mvp;
-layout(location = 0) in vec3 vertexPosition_modelspace;
+layout(location = 0) in vec2 pos;
 
 void main() {
-     gl_Position = mvp * vec4(vertexPosition_modelspace, 1);
+     gl_Position = mvp * vec4((pos + vec2(0.5, 0.5)), 0, 1);
 }