From ecb38f349349ab369383c51a22f430909a7d2ebd Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 14 Apr 2026 12:45:23 +0300
Subject: [PATCH] gg: gg.update_pixel_data() empty buffer still draws (fixes
 #10989)

---
 vlib/gg/streaming_image_gl_test.v             | 41 +++++++++++++++++++
 .../streaming_r8_zero_buffer_issue_10989.vv   | 37 +++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 vlib/gg/streaming_image_gl_test.v
 create mode 100644 vlib/gg/testdata/streaming_r8_zero_buffer_issue_10989.vv

diff --git a/vlib/gg/streaming_image_gl_test.v b/vlib/gg/streaming_image_gl_test.v
new file mode 100644
index 000000000..e1e8479d9
--- /dev/null
+++ b/vlib/gg/streaming_image_gl_test.v
@@ -0,0 +1,41 @@
+// vtest build: macos && !sanitized_job?
+import os
+import stbi
+
+@[direct_array_access]
+fn png_has_non_black_pixels(path string) !bool {
+	img := stbi.load(path)!
+	defer {
+		img.free()
+	}
+	for i in 0 .. img.width * img.height {
+		unsafe {
+			if img.data[i * 4] != 0 || img.data[i * 4 + 1] != 0 || img.data[i * 4 + 2] != 0 {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+fn test_streaming_r8_zero_buffer_stays_black_on_gl_backend() {
+	vexe := @VEXE
+	vroot := os.dir(vexe)
+	sample_path := os.join_path(vroot, 'vlib/gg/testdata/streaming_r8_zero_buffer_issue_10989.vv')
+	temp_dir := os.join_path(os.temp_dir(), 'v_gg_issue_10989_${os.getpid()}')
+	os.mkdir_all(temp_dir) or { panic(err) }
+	defer {
+		os.rmdir_all(temp_dir) or {}
+	}
+	exe_path := os.join_path(temp_dir, 'issue10989_repro')
+	// Force the GL backend so this exercises the packed texture upload path from issue #10989.
+	compile_cmd := '${os.quoted_path(vexe)} -d gg_record -d darwin_sokol_glcore33 -o ${os.quoted_path(exe_path)} ${os.quoted_path(sample_path)}'
+	compile_res := os.execute(compile_cmd)
+	assert compile_res.exit_code == 0, compile_res.output
+	run_cmd := 'VGG_STOP_AT_FRAME=2 VGG_SCREENSHOT_FRAMES=2 VGG_SCREENSHOT_FOLDER=${os.quoted_path(temp_dir)} ${os.quoted_path(exe_path)}'
+	run_res := os.execute(run_cmd)
+	assert run_res.exit_code == 0, run_res.output
+	screenshot_path := os.join_path(temp_dir, 'issue10989_repro_2.png')
+	assert os.exists(screenshot_path)
+	assert png_has_non_black_pixels(screenshot_path)! == false
+}
diff --git a/vlib/gg/testdata/streaming_r8_zero_buffer_issue_10989.vv b/vlib/gg/testdata/streaming_r8_zero_buffer_issue_10989.vv
new file mode 100644
index 000000000..607bd3f53
--- /dev/null
+++ b/vlib/gg/testdata/streaming_r8_zero_buffer_issue_10989.vv
@@ -0,0 +1,37 @@
+module main
+
+import gg
+
+const win_width = 100
+const win_height = 100
+
+struct App {
+mut:
+	gg    &gg.Context = unsafe { nil }
+	image int
+}
+
+fn main() {
+	mut app := &App{}
+	app.gg = gg.new_context(
+		width:        win_width
+		height:       win_height
+		window_title: 'issue 10989'
+		frame_fn:     frame
+		user_data:    app
+		init_fn:      initialize
+	)
+	app.gg.run()
+}
+
+fn initialize(mut app App) {
+	buffer := []u8{len: 10 * 10}
+	app.image = app.gg.new_streaming_image(10, 10, 1, pixel_format: .r8)
+	app.gg.update_pixel_data(app.image, buffer.data)
+}
+
+fn frame(mut app App) {
+	app.gg.begin()
+	app.gg.draw_image_by_id(0, 0, 10, 10, app.image)
+	app.gg.end()
+}
-- 
2.39.5