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fix window extent after creating

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The requested dimensions of a newly created window may be different
from the actual dimensions as the window system may enforce additional
restrictions. This happens, for example, when using Wayland with a
scaling factor of 3 (the default width of 800 is not divisible by 3).

To fix it, just re-query the actual framebuffer size after creating the window.
The GLFW documentation also suggests to do this:

> The created window, framebuffer and context may differ from what you requested,
> as not all parameters and hints are hard constraints. This includes the size of
> the window, especially for full screen windows. To query the actual attributes
> of the created window, framebuffer and context, see glfwGetWindowAttrib,
> glfwGetWindowSize and glfwGetFramebufferSize.

-- https://www.glfw.org/docs/3.3/group__window.html#ga3555a418df92ad53f917597fe2f64aeb

This should be a better fix for #192
This commit is contained in:
Robin Voetter
2025-07-20 09:16:16 +02:00
parent f99c5994dc
commit 39565ca4c3
1 changed files with 22 additions and 5 deletions
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27
examples/triangle.zig
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@@ -63,6 +63,23 @@ pub fn main() !void {
) orelse return error.WindowInitFailed;
defer c.glfwDestroyWindow(window);
// According to the GLFW docs:
//
// > Window systems put limits on window sizes. Very large or very small window dimensions
// > may be overridden by the window system on creation. Check the actual size after creation.
// -- https://www.glfw.org/docs/3.3/group__window.html#ga3555a418df92ad53f917597fe2f64aeb
//
// This happens in practice, for example, when using Wayland with a scaling factor that is not a
// divisor of the initial window size (see https://github.com/Snektron/vulkan-zig/pull/192).
// To fix it, just fetch the actual size here, after the windowing system has had the time to
// update the window.
extent.width, extent.height = blk: {
var w: c_int = undefined;
var h: c_int = undefined;
c.glfwGetFramebufferSize(window, &w, &h);
break :blk .{ @intCast(w), @intCast(h) };
};
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
defer _ = gpa.deinit();
const allocator = gpa.allocator();
@@ -123,6 +140,7 @@ pub fn main() !void {
);
defer destroyCommandBuffers(&gc, pool, allocator, cmdbufs);
var state: Swapchain.PresentState = .optimal;
while (c.glfwWindowShouldClose(window) == c.GLFW_FALSE) {
var w: c_int = undefined;
var h: c_int = undefined;
@@ -136,11 +154,6 @@ pub fn main() !void {
const cmdbuf = cmdbufs[swapchain.image_index];
const state = swapchain.present(cmdbuf) catch |err| switch (err) {
error.OutOfDateKHR => Swapchain.PresentState.suboptimal,
else => |narrow| return narrow,
};
if (state == .suboptimal or extent.width != @as(u32, @intCast(w)) or extent.height != @as(u32, @intCast(h))) {
extent.width = @intCast(w);
extent.height = @intCast(h);
@@ -161,6 +174,10 @@ pub fn main() !void {
framebuffers,
);
}
state = swapchain.present(cmdbuf) catch |err| switch (err) {
error.OutOfDateKHR => Swapchain.PresentState.suboptimal,
else => |narrow| return narrow,
};
c.glfwPollEvents();
}