Android (Adreno 830): changing aspect ratio or resolution crashes the game #72

What happens

On a Galaxy Z Fold 7 (Snapdragon 8 Elite, Adreno 830), changing the aspect ratio or the internal resolution while playing aborts the game. Reproduces on current main (9ca2a76, v0.2.7).

Cause

After a scale or aspect change, rescale() in runtime/src/gfx/vulkan/surfaces.cpp makes a replacement image and copies the old contents into it with resample(), which uses vkCmdBlitImage. resample() checks BLIT_SRC/BLIT_DST and throws Vulkan device cannot blit this surface format when they're missing. The exception isn't caught on the render thread, so the process aborts.

Vulkan doesn't require blit support for any depth/stencil format (BLIT_DST is optional for all of them), and Adreno doesn't report it for some. Desktop drivers and MoltenVK happen to support it, which is why this only shows up on Android. Logging on the Fold 7 shows the formats affected there:

• VK_FORMAT_D32_SFLOAT (126): hit on the first aspect change
• VK_FORMAT_D16_UNORM (124): hit on the first resolution change

The scaled-copy branch of copy_surface_impl() (GX2CopySurface) has the same check and would abort the same way for a scaled depth copy.

Fix (attached patch)

When a depth format can't be blitted, the scaled copy is drawn instead:

• A fullscreen triangle per layer. Each pixel texelFetches the source texel a VK_FILTER_NEAREST blit would pick (the spec's (x+0.5)·src/dst mapping) and writes it with gl_FragDepth.
• Stencil (D32F+S8) is copied one bit per pass: the depth pass zeroes stencil, then 8 passes each write one bit with discard where the source bit is clear. No VK_EXT_shader_stencil_export needed.
• Used by both resample() (so rescale() and read_guest_texels()) and the scaled GX2CopySurface path.
• Devices that can blit keep the blit, so desktop and macOS behavior is unchanged. The first time a format takes the draw path, one log line names it.
• WWHD_VK_DEPTH_COPY=draw forces the draw path on any device, for testing.
• Adds vkCmdSetStencilWriteMask (Vulkan 1.0 core) to loader.h.

Old depth contents survive the resize, so a rescale landing mid-frame doesn't leave a frame depth-testing against garbage. Skipping the copy for unblittable depth formats would avoid the crash too, but only works when the game clears the buffer right after.

Testing

Renderer smoke test (Linux, lavapipe, WWHD_VK_VALIDATION=1): new depth_copy_check(), with the draw path forced:

• D16, D32F and D32F+S8, 2-layer arrays, scaled up (40×24 → 64×37), down (→ 17×11) and same size. Every depth and stencil texel is compared against the nearest-filter mapping.
• A partial region from part of the source (uMax/vMax < 1). Pixels outside the region keep their earlier clear values.
• The real resize path: a screen-shaped D32F+S8 target through a 21:9 aspect change (64×36 → 84×36), then 2× resolution (→ 168×72), then back, checked after each step.
• Full smoke test PASS, zero validation messages. The check fails as expected when the depth lookup is shifted one texel or a stencil bit pass is skipped.

On the Fold 7: aspect ratio Match window (1.11), 16:10, 21:9, 32:9, 16:9, then internal resolution 1.5×, 2×, 3×, 1×, all switched live with no crash.