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viewporter: clamp sub-pixel overflow (#11845)

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Clamps the pending wp_viewport source rect back inside the attached buffer when it misses by <= 1 px, so if clients request something that falls within the 256-increment wl_fixed_from_double precision error it’s still treated as valid.
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omar 2025-09-28 04:14:43 +10:00 • committed by GitHub
parent 6f1d2e771d
commit ef479ff539
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1 changed files with 25 additions and 2 deletions
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27
src/protocols/Viewporter.cpp
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@ -1,6 +1,7 @@
#include "Viewporter.hpp"
#include "core/Compositor.hpp"
#include <algorithm>
#include <cmath>
CViewportResource::CViewportResource(SP<CWpViewport> resource_, SP<CWLSurfaceResource> surface_) : m_surface(surface_), m_resource(resource_) {
if UNLIKELY (!good())
@ -60,9 +61,31 @@ CViewportResource::CViewportResource(SP<CWpViewport> resource_, SP<CWLSurfaceRes
return;
if (m_surface->m_pending.viewport.hasSource) {
auto& src = m_surface->m_pending.viewport.source;
auto& src = m_surface->m_pending.viewport.source;
const auto& size = m_surface->m_pending.bufferSize;
if (src.w + src.x > m_surface->m_pending.bufferSize.x || src.h + src.y > m_surface->m_pending.bufferSize.y) {
if (size.x <= 0.0 || size.y <= 0.0)
return;
constexpr wl_fixed_t MAX_TOLERANCE = 1 << 8; // wl_fixed 1.0 = 256
auto clampAxis = [&](double& start, double& length, double limit) -> bool {
const double originalStart = start;
const double originalEnd = start + length;
const double clampedStart = std::clamp(start, 0.0, std::max(0.0, limit));
const double clampedEnd = std::clamp(originalEnd, 0.0, std::max(0.0, limit));
const wl_fixed_t startDelta = std::abs(wl_fixed_from_double(clampedStart) - wl_fixed_from_double(originalStart));
const wl_fixed_t endDelta = std::abs(wl_fixed_from_double(clampedEnd) - wl_fixed_from_double(originalEnd));
if (startDelta > MAX_TOLERANCE || endDelta > MAX_TOLERANCE)
return false;
start = clampedStart;
length = clampedEnd - clampedStart;
return length > 0.0;
};
if (!clampAxis(src.x, src.w, size.x) || !clampAxis(src.y, src.h, size.y)) {
m_resource->error(WP_VIEWPORT_ERROR_BAD_VALUE, "Box doesn't fit");
m_surface->m_pending.rejected = true;
return;