67 lines
2.8 KiB
Markdown
67 lines
2.8 KiB
Markdown
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# STP : Semi-Transparency usage
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This example shows the various way of converting an image with transparency to a TIM and use it in code.
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It also shows the effect of activating Semi-Transparency on a primitive textured with those images.
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Use the `SELECT` button to switch primitive semi-transparency on and off.
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It also features a few C struct to facilitate access to the TIM file / pixel data.
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You can use Lameguy64's [img2tim](https://github.com/Lameguy64/img2tim) tool to convert most of image formats to the psx [TIM format.](https://github.com/ABelliqueux/nolibgs_hello_worlds/tree/main/TIM).
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## Semi-transparency rates
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You can find another example with the various transparency rates demoed here : https://github.com/ABelliqueux/nolibgs_hello_worlds/tree/main/hello_cubetex_stp
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## Important
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**By default, the PSX will consider black pixels (0,0,0,0) as transparent**.
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In order to display those black pixels as black, you have to set the STP on black (1,0,0,0).
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Black pixels and non-black pixels with the STP bit will display as semi-transparent when using `SetSemiTrans()`.
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## STP on black
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Use this to display black pixels as black, not transparent.
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The **inverted** alpha mask of the TIM corresponds to the position of black (0,0,0) pixels in the image.
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```bash
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img2tim -b -org 640 0 -o stpOnBlack.tim av.png
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```
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## STP on non-black
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Black pixels will be considered as transparent, and non-black pixels will receive semi-transparency with `SetSemiTrans()`.
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The alpha mask of the TIM corresponds to the position of non-black (n,n,n) pixels in the image.
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Additionally, a setting allows you to define the RGB value to be considered transparent ; `-tcol` . This does not set any STP flag.
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```bash
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img2tim -t -org 320 0 -o stpOnNonBlack.tim av.png
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```
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## Use alpha channel
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The alpha mask of the TIM corresponds to the existing alpha channel of the image (PNG, GIF, TGA, TIFF).
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Additionally, a setting allows you to define the threshold for the alpha value to be considered transparent ; `-alpt` . This does not set any STP flag.
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```bash
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img2tim -usealpha -org 640 256 -o stpOnNonBlack.tim av.png
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```
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## Use color index
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When using 8/4bpp palettized images, you can specify the index number of the color to be considered transparent. This does not set any STP flag.
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You can set the STP bit by CLUT color with PsyQ's `TIMTOOL.EXE`. This allows you do do cool stuff like oly having specific colors being rendered as semi-transparent by `SetSemiTrans()`.
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```bash
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img2tim -b -bpp 8 -tindex 0 -org 640 256 -plt 0 481 -o stpOnColIndex.tim av8.png
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```
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## Black transparency work-around
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Using a pseudo-black color with one of the channels value to 10, i.e : `255,255,10` can be done so you dont have to set the STP bit on full black.
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This allows you to keep the pseudo-black opaque when using `SetSemiTrans()`.
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