LOS ray cast from the edge of an obstacle has varied intersection results

CodyRockwell commented 6 months ago

Problem description

When casting a ray that starts exactly at the edge of an obstacle, depending on the angle and position of the ray, the ray may not trigger the 'Ray Intersected' condition. If the ray does intersect the obstacle, the 'HitX' and 'HitY' values may return 'NaN'.

Attach a .c3p

https://drive.google.com/file/d/1by8JDRxsZqc5FD1mkH_5Hgx1vZfMjYzN/view?usp=sharing

Steps to reproduce

Open the .c3p and observe
The numbered RayCaster sprites all cast rays down (90 degrees). Their opacity flickers to indicate when 'Ray Intersected' is triggered
Any RayCaster whose ray intersects the obstacle creates a green line from the rays starting point to its ending point

Observed result

RayCaster sprites 0 and 8 don't register a hit at all.
Sprites 2, 4 and 7 are the only ones that have 'HitX' and 'HitY' values that are not 'NaN'.

Expected result

If 'Ray Intersected' is triggered, then 'HitX' and 'HitY' should have a numerical value.
Rays that align with the angle of an obstacles edge (rays from 0, 1, 4, 5, and 8) should either all trigger 'Ray Intersected' or not trigger it, rather than only certain ones triggering it.

More details

Affected browsers/platforms: Chrome

First affected release: 388.2

System details

View details

Platform information Product: Construct 3 r388.2 (stable) Browser: Chrome 124.0.6367.119 Browser engine: Chromium Context: webapp Operating system: Windows 11 Device type: desktop Device pixel ratio: 1 Logical CPU cores: 12 Approx. device memory: 8 GB User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36 Language setting: en-US Local storage Storage quota (approx): 558 gb Storage usage (approx): 2.1 gb (0.4%) Persistant storage: No Browser support notes This list contains missing features that are not required, but could improve performance or user experience if supported. Nothing is missing. Everything is OK! WebGL information Version string: WebGL 2.0 (OpenGL ES 3.0 Chromium) Numeric version: 2 Supports NPOT textures: yes Supports GPU profiling: no Supports highp precision: yes Vendor: Google Inc. (NVIDIA) Renderer: ANGLE (NVIDIA, NVIDIA GeForce RTX 3060 (0x00002487) Direct3D11 vs_5_0 ps_5_0, D3D11) Major performance caveat: no Maximum texture size: 16384 Point size range: 1 to 1024 Extensions: EXT_clip_control EXT_color_buffer_float EXT_color_buffer_half_float EXT_conservative_depth EXT_depth_clamp EXT_disjoint_timer_query_webgl2 EXT_float_blend EXT_polygon_offset_clamp EXT_texture_compression_bptc EXT_texture_compression_rgtc EXT_texture_filter_anisotropic EXT_texture_mirror_clamp_to_edge EXT_texture_norm16 KHR_parallel_shader_compile NV_shader_noperspective_interpolation OES_draw_buffers_indexed OES_texture_float_linear OVR_multiview2 WEBGL_blend_func_extended WEBGL_clip_cull_distance WEBGL_compressed_texture_s3tc WEBGL_compressed_texture_s3tc_srgb WEBGL_debug_renderer_info WEBGL_debug_shaders WEBGL_lose_context WEBGL_multi_draw WEBGL_polygon_mode WEBGL_provoking_vertex WEBGL_stencil_texturing Audio information System sample rate: 48000 Hz Output channels: 2 Output interpretation: speakers Supported decode formats: WebM Opus (audio/webm;codecs=opus) WebM Vorbis (audio/webm;codecs=vorbis) MPEG-4 Opus (audio/mp4;codecs=opus) MPEG-4 AAC (audio/mp4;codecs=mp4a.40.2) MP3 (audio/mpeg) FLAC (audio/flac) PCM WAV (audio/wav;codecs=1) Supported encode formats: WebM Opus (audio/webm;codecs=opus) Video information Supported decode formats: WebM AV1 (video/webm;codecs=av01.0.00M.08) WebM VP9 (video/webm;codecs=vp9) WebM VP8 (video/webm;codecs=vp8) MPEG-4 AV1 (video/mp4;codecs=av01.0.00M.08) MPEG-4 H.265 (video/mp4;codecs=hev1.1.2.L93.B0) MPEG-4 H.264 (video/mp4;codecs=avc1.420034) Supported encode formats: WebM AV1 (video/webm;codecs=av01.0.00M.08) WebM VP9 (video/webm;codecs=vp9) WebM VP8 (video/webm;codecs=vp8) WebM H.264 (video/webm;codecs=avc1.420034)

WilsonPercival commented 6 months ago

I may be wrong, but if we try to calculate the intersection point of two vertical lines using Cramer's method, we will get NaN due to the division by 0. Perhaps the same thing happens in the raycast process.

issue7995.zip

AshleyScirra commented 6 months ago

Computers do fractional (floating point) calculations with limited precision. This introduces rounding errors with any type of calculation (in any software, on any hardware). This means this kind of intermittent or unreliable result at extreme edge cases is normal in software. You generally just have to design your game around it as there is no feasible workaround. See 0.30000000000000004.com.

Scirra / Construct-bugs