renderer/opengl: draw custom shaders, simplified

src/renderer/OpenGL.zig

@@ -1410,6 +1410,9 @@ pub fn drawFrame(self: *OpenGL, surface: *apprt.Surface) !void {
     // Draw our terminal cells
     try self.drawCellProgram(&gl_state);
 
+    // Draw our custom shaders
+    try self.drawCustomPrograms(&gl_state);
+
     // Swap our window buffers
     switch (apprt.runtime) {
         apprt.glfw => surface.window.swapBuffers(),
@@ -1418,6 +1421,20 @@ pub fn drawFrame(self: *OpenGL, surface: *apprt.Surface) !void {
     }
 }
 
+fn drawCustomPrograms(
+    self: *OpenGL,
+    gl_state: *const GLState,
+) !void {
+    _ = self;
+
+    for (gl_state.custom_programs) |program| {
+        // Bind our cell program state, buffers
+        const bind = try program.bind();
+        defer bind.unbind();
+        try gl.drawElementsInstanced(gl.c.GL_TRIANGLES, 6, gl.c.GL_UNSIGNED_BYTE, 1);
+    }
+}
+
 /// Runs the cell program (shaders) to draw the terminal grid.
 fn drawCellProgram(
     self: *OpenGL,

src/renderer/opengl/CustomProgram.zig

@@ -84,3 +84,32 @@ pub fn deinit(self: CustomProgram) void {
     self.vao.destroy();
     self.program.destroy();
 }
+
+pub fn bind(self: CustomProgram) !Binding {
+    const program = try self.program.use();
+    errdefer program.unbind();
+
+    const vao = try self.vao.bind();
+    errdefer vao.unbind();
+
+    const ebo = try self.ebo.bind(.element_array);
+    errdefer ebo.unbind();
+
+    return .{
+        .program = program,
+        .vao = vao,
+        .ebo = ebo,
+    };
+}
+
+pub const Binding = struct {
+    program: gl.Program.Binding,
+    vao: gl.VertexArray.Binding,
+    ebo: gl.Buffer.Binding,
+
+    pub fn unbind(self: Binding) void {
+        self.ebo.unbind();
+        self.vao.unbind();
+        self.program.unbind();
+    }
+};

src/renderer/shaders/custom.v.glsl

@@ -2,7 +2,7 @@
 
 void main(){
     vec2 position;
-    position.x = (gl_VertexID == 0 || gl_VertexID == 1) ? 1. : 0.;
-    position.y = (gl_VertexID == 0 || gl_VertexID == 3) ? 0. : 1.;
+    position.x = (gl_VertexID == 0 || gl_VertexID == 1) ? -1. : 1.;
+    position.y = (gl_VertexID == 0 || gl_VertexID == 3) ? 1. : -1.;
     gl_Position = vec4(position.xy, 0.0f, 1.0f);
 }

src/renderer/shaders/temp.f.glsl

@@ -3,6 +3,10 @@
 layout(location = 0) out vec4 out_FragColor;
 
 void main() {
-    // read
-    out_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
+    // red
+    //out_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
+
+    // maze
+    vec4 I = gl_FragCoord;
+    out_FragColor = vec4(3)*modf(I*.1,I)[int(length(I)*1e4)&1];
 }