fix(draw): fix "blend_non_normal_pixel: Not supported blend mode" issue when using lv_demo_smartwatch which compiled by MSVC

[MouriNaruto]

In the recent days, one of LVGL Visual Studio repository users told me that there are some issues mentioned in the screenshot when he trying to use lv_demo_smartwatch.

This issue seems something familiar for me. So, I solve the issue for that user quickly. I think I should create a PR instead of an issue, and hope the issue can be fixed as soon as possible.

Kenji Mouri

[uLipe]

@MouriNaruto could you describe why the type of the blend mode is the cause of the issue above?

Thank you :)

[MouriNaruto]

@MouriNaruto could you describe why the type of the blend mode is the cause of the issue above?

Thank you :)

Because MSVC will consider the enum types as int32_t (not the uint32_t you think) by default.

Kenji Mouri

[MouriNaruto]

The constant-expression must have int type and can be negative.

Reference: https://learn.microsoft.com/en-us/cpp/c-language/c-enumeration-declarations?view=msvc-170#syntax

It also seems that ISO C (until C23 because C23 can define custom integer type for enum like C++) also follows that.

https://en.cppreference.com/w/c/language/enum

Kenji Mouri

[uLipe]

@MouriNaruto thanks for clarifying it.

[MouriNaruto]

@kisvegabor @liamHowatt ping

Kenji Mouri

[MouriNaruto]

@kisvegabor @uLipe @liamHowatt Ping

Kenji Mouri