Bug 479462

Summary: Default pressure curve gives uneven on left part of tablet - S-pen
Product: [Applications] krita Reporter: Zayastarcaller
Component: Brush Engine/ShapeAssignee: Krita Bugs <krita-bugs-null>
Status: RESOLVED NOT A BUG    
Severity: normal CC: info, lynx.mw+kde
Priority: NOR    
Version: 5.2.2   
Target Milestone: ---   
Platform: Android   
OS: Android 13.x   
Latest Commit: Version Fixed In:
Sentry Crash Report:
Attachments: images containing the issue.

Description Zayastarcaller 2024-01-06 12:08:00 UTC 
Created attachment 164704 [details]
images containing the issue.

SUMMARY
When using the my tablet (samsung galaxy tab s8 ultra) to draw, on the left side of the screen there seems to be a bug where on certain spots it gives uneven pressure, I have tested on two different tablets, S8 ultra, and S9 ultra, both exhibit the same issue with the default pressure curve of the tools that have anything else than a linear curve, see attached photos.

Troubleshooting includes:
1. tested different tablet with same version of krita, -> same issue
2. tested with a different S-pen on both of those tablets -> same issue
3. uninstalled krita, removing all data associated with it, and reinstalled it -> same issue
4. tested different brushes and tools in krita, brushes with non-linear curves exhibits the problems.
5. made brushes have a linear curve from 0 - 100, with just 2 points -> issue resolved as a bypass


STEPS TO REPRODUCE
1. Have a tablet with wacom support on android 13.x (I believe any android tablet with wacom style pens work)
2. set brush pixel size to be 50 or more so problem can be visible
3. use any pen that has a different curve for their size than linear, for example the fountain pen.
4. draw lines going down from the top, with an even pressure and observe the pressure changing by itself.

OBSERVED RESULT
see images attached

EXPECTED RESULT
expected result is to have the pen pressure in that region not change as you move over a specific part with even pressure, see images for explanation.

SOFTWARE/OS VERSIONS
Android 13
Qt Version:  5.15.7

ADDITIONAL INFORMATION

Krita

 Version: 5.2.2
 Hidpi: true

Qt

  Version (compiled): 5.15.7
  Version (loaded): 5.15.7

OS Information

  Build ABI: arm64-little_endian-lp64
  Build CPU: arm64
  CPU: arm64
  Kernel Type: linux
  Kernel Version: 5.10.136-android12-9-27102101-abX906BXXS5BWI1
  Pretty Productname: Android (13.0)
  Product Type: android
  Product Version: 13.0
  Product Model: Samsung SM-X906B

Locale

  Languages: en_GB, en_Latn_GB
  C locale: C.UTF-8
  QLocale current: en
  QLocale system: en
  QTextCodec for locale: UTF-8

OpenGL Info
 
  Vendor: "Qualcomm" 
  Renderer: "Adreno (TM) 730" 
  Driver version: "OpenGL ES 3.2 V@0615.0 (GIT@5a00bbd4b7, I0f5aa60515, 1673930385) (Date:01/16/23)" 
  Shading language: "OpenGL ES GLSL ES 3.20" 
  Requested format: QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::DoubleBuffer, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile QSurfaceFormat::NoProfile) 
  Current format: QSurfaceFormat(version 3.2, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples 0, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile QSurfaceFormat::NoProfile) 
  GL version: 3.2 
  Supports deprecated functions false 
  Is OpenGL ES: true 
  supportsBufferMapping: true 
  supportsBufferInvalidation: false 
  forceDisableTextureBuffers: false 
  Extensions: 
     GL_EXT_clip_control 
     GL_KHR_texture_compression_astc_hdr 
     GL_OES_texture_compression_astc 
     GL_EXT_primitive_bounding_box 
     GL_EXT_protected_textures 
     GL_EXT_texture_sRGB_decode 
     GL_OES_shader_multisample_interpolation 
     GL_KHR_robust_buffer_access_behavior 
     GL_QCOM_validate_shader_binary 
     GL_OES_framebuffer_object 
     GL_EXT_color_buffer_float 
     GL_OES_depth24 
     GL_EXT_discard_framebuffer 
     GL_QCOM_texture_foveated2 
     GL_EXT_draw_buffers_indexed 
     GL_OES_texture_float 
     GL_ARM_shader_framebuffer_fetch_depth_stencil 
     GL_OES_texture_npot 
     GL_EXT_read_format_bgra 
     GL_OES_texture_half_float_linear 
     GL_QCOM_tiled_rendering 
     GL_EXT_memory_object_fd 
     GL_OES_sample_shading 
     GL_OES_EGL_image 
     GL_EXT_texture_buffer 
     GL_EXT_fragment_invocation_density 
     GL_EXT_external_buffer 
     GL_EXT_texture_type_2_10_10_10_REV 
     GL_OES_vertex_array_object 
     GL_ANDROID_extension_pack_es31a 
     GL_EXT_sRGB 
     GL_EXT_texture_cube_map_array 
     GL_KHR_texture_compression_astc_ldr 
     GL_EXT_debug_label 
     GL_OES_texture_3D 
     GL_OES_standard_derivatives 
     GL_OES_rgb8_rgba8 
     GL_EXT_disjoint_timer_query 
     GL_OES_texture_half_float 
     GL_EXT_blit_framebuffer_params 
     GL_EXT_EGL_image_storage 
     GL_EXT_gpu_shader5 
     GL_EXT_buffer_storage 
     GL_QCOM_shader_framebuffer_fetch_noncoherent 
     GL_OES_vertex_half_float 
     GL_EXT_shader_non_constant_global_initializers 
     GL_OES_shader_image_atomic 
     GL_EXT_shader_io_blocks 
     GL_OES_EGL_image_external_essl3 
     GL_QCOM_shader_framebuffer_fetch_rate 
     GL_QCOM_render_shared_exponent 
     GL_QCOM_texture_foveated 
     GL_OES_EGL_image_external 
     GL_AMD_compressed_ATC_texture 
     GL_OES_texture_storage_multisample_2d_array 
     GL_EXT_sRGB_write_control 
     GL_QCOM_shading_rate 
     GL_EXT_EGL_image_array 
     GL_EXT_copy_image 
     GL_KHR_blend_equation_advanced_coherent 
     GL_OES_texture_float_linear 
     GL_OES_depth_texture_cube_map 
     GL_QCOM_motion_estimation 
     GL_QCOM_YUV_texture_gather 
     GL_EXT_tessellation_shader 
     GL_KHR_blend_equation_advanced 
     GL_EXT_texture_sRGB_R8 
     GL_EXT_texture_format_sRGB_override 
     GL_EXT_EGL_image_external_wrap_modes 
     GL_EXT_clip_cull_distance 
     GL_EXT_texture_format_BGRA8888 
     GL_EXT_texture_norm16 
     GL_OES_surfaceless_context 
     GL_OES_element_index_uint 
     GL_QCOM_frame_extrapolation 
     GL_KHR_debug 
     GL_OES_EGL_sync 
     GL_OES_compressed_ETC1_RGB8_texture 
     GL_OES_texture_view 
     GL_OES_texture_stencil8 
     GL_EXT_memory_object 
     GL_EXT_robustness 
     GL_OVR_multiview2 
     GL_OVR_multiview_multisampled_render_to_texture 
     GL_EXT_shader_framebuffer_fetch 
     GL_EXT_blend_func_extended 
     GL_EXT_texture_filter_anisotropic 
     GL_OES_packed_depth_stencil 
     GL_OES_get_program_binary 
     GL_EXT_YUV_target 
     GL_IMG_texture_filter_cubic 
     GL_OES_sample_variables 
     GL_EXT_multisampled_render_to_texture2 
     GL_EXT_texture_border_clamp 
     GL_NV_shader_noperspective_interpolation 
     GL_KHR_no_error 
     GL_QCOM_alpha_test 
     GL_EXT_geometry_shader 
     GL_EXT_multisampled_render_to_texture 
     GL_EXT_debug_marker 
     GL_EXT_color_buffer_half_float 
     GL_OES_depth_texture 
     GL_OVR_multiview 
     GL_QCOM_texture_foveated_subsampled_layout 

QPA OpenGL Detection Info 
  supportsDesktopGL: false 
  supportsOpenGLES: true 
  isQtPreferOpenGLES: true 
  Detected renderers: 
    (Supported) Adreno (TM) 730 (OpenGL ES 3.2 V@0615.0 (GIT@5a00bbd4b7, I0f5aa60515, 1673930385) (Date:01/16/23))  

useBufferInvalidation (config option): false


Hardware Information

  GPU Acceleration: auto
  Memory: 7300 Mb
  Number of Cores: 8
  Swap Location: /data/data/org.krita/cache
  Built for: arm64+neon
  Base instruction set: arm64+neon
  Supported instruction sets: arm64+neon arm32+neon avx512bw avx512dq avx512cd avx512f fma3+avx2 avx2 fma3+avx avx fma4 fma3+sse4.2 sse4.2 sse4.1 ssse3 sse3 sse2 

Current Settings

  Current Swap Location: /data/data/org.krita/cache
  Current Swap Location writable: true
  Undo Enabled: true
  Undo Stack Limit: 200
  Use OpenGL: true
  Use OpenGL Texture Buffer: true
  Disable Vector Optimizations: false
  Disable AVX Optimizations: false
  Canvas State: OPENGL_NOT_TRIED
  Autosave Interval: 420
  Use Backup Files: true
  Number of Backups Kept: 1
  Backup File Suffix: ~
  Backup Location: Same Folder as the File
  Backup Location writable: false
  Resource Location: 
  Use Win8 Pointer Input: false
  Use RightMiddleTabletButton Workaround: false
  Levels of Detail Enabled: false
  Use Zip64: false


Display Information
Number of screens: 1
 Screen: 0
  Name: 
  Depth: 32
  Scale: 2
  Physical DPI120.01
  Logical DPI72
  Physical Size: 314, 182
  Position: 0, 0
  Resolution in pixels: 1480x862
  Manufacturer: 
  Model: 
  Refresh Rate: 60
  Serial Number: 

Current Settings

  Current Swap Location: /data/data/org.krita/cache
  Current Swap Location writable: true
  Undo Enabled: true
  Undo Stack Limit: 200
  Use OpenGL: true
  Use OpenGL Texture Buffer: true
  Disable Vector Optimizations: false
  Disable AVX Optimizations: false
  Canvas State: TRY_OPENGL
  Autosave Interval: 420
  Use Backup Files: true
  Number of Backups Kept: 1
  Backup File Suffix: ~
  Backup Location: Same Folder as the File
  Backup Location writable: false
  Resource Location: /storage/emulated/0/Android/data/org.krita/files
  Use Win8 Pointer Input: false
  Use RightMiddleTabletButton Workaround: false
  Levels of Detail Enabled: false
  Use Zip64: false



---------------------
================================================================================
SESSION: 06 Jan 2024 12:05:30 +0100. Executing /data/app/~~jWEmgSF6Nf7iAVWLDgwRIQ==/org.krita-zvB7PZ1VIDojuZ829RZzQA==/lib/arm64/libkrita_arm64-v8a.so

Krita Version: 5.2.2, Qt version compiled: 5.15.7, loaded: 5.15.7. Process ID: 8957
-- -- -- -- -- -- -- --
06 Jan 2024 12:05:30 +0100: Style: fusion. Available styles: android, Windows, Fusion
06 Jan 2024 12:05:31 +0100: Creating database from scratch (database didn't exist, new schema version: 0.0.17).
06 Jan 2024 12:05:44 +0100: Created image "Unnamed", 2480 * 3508 pixels, 300 dpi. Color model: 8-bit integer/channel RGB/Alpha (sRGB-elle-V2-srgbtrc.icc). Layers: 2
06 Jan 2024 12:07:56 +0100: Converting from application/x-krita to application/x-krita. Location: /storage/emulated/0/Android/data/org.krita/files/Documents/krita-backup/.krita-8957-document_0-autosave.kra. Real location: /storage/emulated/0/Android/data/org.krita/files/Documents/krita-backup/.krita-8957-document_0-autosave.kra. Batchmode: 0. Configuration: none
06 Jan 2024 12:12:35 +0100: Removing autosave file: /storage/emulated/0/Android/data/org.krita/files/Documents/krita-backup/.krita-8957-document_0-autosave.kra
06 Jan 2024 12:13:11 +0100: Created image "Unnamed", 2480 * 3508 pixels, 300 dpi. Color model: 8-bit integer/channel RGB/Alpha (sRGB-elle-V2-srgbtrc.icc). Layers: 2

---------------------
Comment 1 David REVOY 2024-01-06 16:12:08 UTC 
As far as I know, Krita manages the tablet equally across the canvas. So if you experience a bug that affects only a part or specific spot of the canvas, e.g. a pressure change that affects only a region as you describe, it's most likely caused by bad engineering at the hardware level. 
I'm sorry. 
It could be bad electromagnetic shielding of the display, or a connector in that area that is leaking and affecting the pressure sensitivity, 
I have never seen this happen specifically to "pressure only" with Wacom's EMR (electromagnetic resonance) based device. (I'm assuming here that the Samsung Android tablets use EMR technology for their pen). The classic problem I see when bad shielding is done at the engineering of the tablet is mostly line shaking, and a line jittering with the noise. So, I'm not sure what is exactly happening in your case. 

Can you reproduce the issue with another painting software using pressure sensitivity? 
That would at least confirm it is a bug hardware specific.
Comment 2 Zayastarcaller 2024-01-06 16:22:14 UTC 
(In reply to David REVOY from comment #1)
> As far as I know, Krita manages the tablet equally across the canvas. So if
> you experience a bug that affects only a part or specific spot of the
> canvas, e.g. a pressure change that affects only a region as you describe,
> it's most likely caused by bad engineering at the hardware level. 
> I'm sorry. 
> It could be bad electromagnetic shielding of the display, or a connector in
> that area that is leaking and affecting the pressure sensitivity, 
> I have never seen this happen specifically to "pressure only" with Wacom's
> EMR (electromagnetic resonance) based device. (I'm assuming here that the
> Samsung Android tablets use EMR technology for their pen). The classic
> problem I see when bad shielding is done at the engineering of the tablet is
> mostly line shaking, and a line jittering with the noise. So, I'm not sure
> what is exactly happening in your case. 
> 
> Can you reproduce the issue with another painting software using pressure
> sensitivity? 
> That would at least confirm it is a bug hardware specific.

I have tried a few different ones, namely hipaint, Medibang, sketchbook (from Autodesk I think) I have not experienced any problems in those applications. I also have a video of the issue, to show own it appears.
Comment 3 Zayastarcaller 2024-01-06 20:04:49 UTC 
Actually please disregard this report, I've done more testing, and it turns out there is a magnetic force in the tablet around that area and I tested with some more drawing software, it seems it is present on those too, albeit less noticeable, I am sorry for making a report on something that seems to be with the tablet.
Comment 4 Bug Janitor Service 2024-01-07 03:46:28 UTC 
Thanks for your comment!

Automatically switching the status of this bug to REPORTED so that the KDE team
knows that the bug is ready to get confirmed.

In the future you may also do this yourself when providing needed information.