gpu/headless: move package app/headless

Package headless is more about rendering that windows. Move it
accordingly.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/headless/headless_macos.m

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// +build darwin,!ios
+
+@import AppKit;
+@import OpenGL;
+@import OpenGL.GL;
+@import OpenGL.GL3;
+
+#include <CoreFoundation/CoreFoundation.h>
+#include "_cgo_export.h"
+
+void gio_headless_releaseContext(CFTypeRef ctxRef) {
+	CFBridgingRelease(ctxRef);
+}
+
+CFTypeRef gio_headless_newContext(void) {
+	NSOpenGLPixelFormatAttribute attr[] = {
+		NSOpenGLPFAOpenGLProfile, NSOpenGLProfileVersion3_2Core,
+		NSOpenGLPFAColorSize,     24,
+		NSOpenGLPFAAccelerated,
+		// Opt-in to automatic GPU switching. CGL-only property.
+		kCGLPFASupportsAutomaticGraphicsSwitching,
+		NSOpenGLPFAAllowOfflineRenderers,
+		0
+	};
+	NSOpenGLPixelFormat *pixFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes:attr];
+	if (pixFormat == nil) {
+		return NULL;
+	}
+	NSOpenGLContext *ctx = [[NSOpenGLContext alloc] initWithFormat:pixFormat shareContext:nil];
+	return CFBridgingRetain(ctx);
+}
+
+void gio_headless_clearCurrentContext(CFTypeRef ctxRef) {
+	NSOpenGLContext *ctx = (__bridge NSOpenGLContext *)ctxRef;
+	CGLUnlockContext([ctx CGLContextObj]);
+	[NSOpenGLContext clearCurrentContext];
+}
+
+void gio_headless_makeCurrentContext(CFTypeRef ctxRef) {
+	NSOpenGLContext *ctx = (__bridge NSOpenGLContext *)ctxRef;
+	[ctx makeCurrentContext];
+	CGLLockContext([ctx CGLContextObj]);
+}
+
+void gio_headless_prepareContext(CFTypeRef ctxRef) {
+	// Bind a default VBA to emulate OpenGL ES 2.
+	GLuint defVBA;
+	glGenVertexArrays(1, &defVBA);
+	glBindVertexArray(defVBA);
+	glEnable(GL_FRAMEBUFFER_SRGB);
+}