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@@ -77,21 +77,117 @@ extern u8 LayerMask; // mask of active layers
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/**
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* @addtogroup LayersGroup
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* @details The display of the image by the PicoVGA library is performed by the PIO processor controller. PIO0 is used.
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* The other controller, PIO1, is unused and can be used for other purposes. PIO0 contains a 4 state machine, SM0 to SM3.
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* The other controller, PIO1, is unused and can be used for other purposes. PIO0 contains a 4 state machines, SM0 to SM3.
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* All PIO0 state machines use a common program of 32 instructions. Each state machine serves 1 overlay layer. SM0 services
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* base layer 0, along with servicing the synchronization signal. The base layer service program consists of 15 instructions,
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* starting at offset 17. This part of the program is immutable and is always used. The other 3 layers, 1 to 3, SM1 to SM3,
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* starting at offset 17. This part of the program is immutable and is always used. However, the other 3 layers, 1 to 3, SM1 to SM3,
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* use the other part of the program memory, 17 instructions starting at address 0. This part may change, depending on the mode
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* of the overlay layers. All 3 overlay layers use a common program and must therefore operate in the same display mode. Some
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* overlay modes use the same program and can be shared - see the table below for details.
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* @note Only base layer 0 can contain segments in different formats. Overlay layers 1 to 3 are independent of the base layer
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* format, sharing only the total display area with the base layer, but using their own image format, for which only the
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* coordinates and dimensions are specified.
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* @par
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* Overlay layers can use one of the following programs:
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*
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* <h3>Overlay layers can use one of the following programs:</h3>
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* * <b>LAYERPROG_BASE</b> - The base layer 0 program. Cannot be used for overlay layers. Using the parameter
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* for an overlay layer means that the layer is inactive (not using the program).
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* * <b>LAYERPROG_KEY</b> - Layer with key color. The specified color is replaced by transparency.
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* * <b>LAYERPROG_BLACK</b> - Transparency with black color. Black is replaced by transparency. Compared to the previous mode,
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* the advantage is less demanding on processor speed.
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* * <b>LAYERPROG_WHITE</b> - transparency with white colour. It is faster like the previous function and is suitable for use
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* where black needs to be preserved but white can be omitted. When preparing the image, the image is not copied from Flash to
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* RAM with the memcpy function, but the CopyWhiteImg() function is used. The function ensures that the pixels of the copied
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* image are incremented by 1. This changes the white color (with a value of 255) to black (with a value of 0). From this point
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* on, the image is treated as if it had transparency with black - e.g. the black color is specified for the sprite rendering
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* function. Only when the image enters the program in PIO0, the program makes the pixel transparent as in the case of black,
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* but at the same time decrements the pixel value. This reverts the colors back to the original value, the black color becomes
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* black and the white color has been used as transparency.
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* * <b>LAYERPROG_MONO</b> - This programme includes 2 sub-programmes. The first is the display of a monochrome image. For each
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* bit of image data, either the selected image color is displayed or the corresponding pixel is transparent. This mode is used
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* in the Oscilloscope example to display a grid across the oscilloscope screen. The second subroutine is to display a color
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* image without transparency. The color pixels are displayed as they are, with no transparency option, but the dimensions of
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* the image rectangle and its coordinate on the display can be defined. Thus, a sort of analogy of a single rectangular sprite
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* without transparency.
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* * <b>LAYERPROG_RLE</b> - RLE compression mode. RLE compression is not a universally valid format. It means that the data
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* contains segment length information. In this case, the image data of PicoVGA library contain directly instructions for the
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* PIO program. More specifically, the image data is interleaved with the jump addresses inside the program. The image is
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* prepared using the RaspPicoRle program and is strongly coupled to the layer program used. If, for example, the instructions
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* in the program were shifted, the RLE compression format would stop working. This is also why the program for base layer 0
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* is placed at the end of the program memory and the overlay layer programs at the beginning - to reduce the chance that
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* changes in the program will change the location of the program in memory, at which point RLE compression would stop working.
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* After modifying the RLE program in PIO, the conversion program must also be updated.
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*
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* The desired mode of each overlay layer is specified in the video mode definition using the VgaCfg() function. The layer mode
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* is used to derive the program and function used to operate the layer rendering. Multiple layer modes can share the same
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* program type. Layer modes have different state machine timing requirements. The configuration function takes this into
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* account and adjusts the processor frequency accordingly.
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*
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* <h3>Modes of overlay layers:</h3>
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*
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* *WHITE modes using white transparent color require image preparation using CopyWhiteImg() as specified for LAYERPROG_WHITE.
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* * <b>LAYERMODE_BASE</b> - Indicates base layer mode 0. Cannot be used for an overlay layer, but is used to indicate an inactive
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* disabled overlay layer.
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* * <b>LAYERMODE_KEY</b> - The layer with the specified key color.
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* * <b>LAYERMODE_BLACK</b> - Layer with black key color.
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* * <b>LAYERMODE_WHITE</b> - Layer with white key color.
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* * <b>LAYERMODE_MONO</b> - Monochromatic image.
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* * <b>LAYERMODE_COLOR</b> - Colour image (without transparency).
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* * <b>LAYERMODE_RLE</b> - Image with RLE compression.
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* * <b>LAYERMODE_SPRITEKEY</b> - Sprays with the specified key color.
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* * <b>LAYERMODE_SPRITEBLACK</b> - Sprays with black key color.
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* * <b>LAYERMODE_SPRITEWHITE</b> - Sprays with white key color.
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* * <b>LAYERMODE_FASTSPRITEKEY</b> - Fast sprites with the specified key colour.
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* * <b>LAYERMODE_FASTSPRITEBLACK</b> - Fast sprites with black key colour.
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* * <b>LAYERMODE_FASTSPRITEWHITE</b> - Fast sprites with white key colour.
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* * <b>LAYERMODE_PERSPKEY</b> - Image with transformation matrix with specified key color.
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* * <b>LAYERMODE_PERSPBLACK</b> - Image with transformation matrix with black key color.
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* * <b>LAYERMODE_PERSPWHITE</b> - Image with transformation matrix with white key color.
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* * <b>LAYERMODE_PERSP2KEY</b> - Image with transformation matrix with specified key color and doubled width.
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* * <b>LAYERMODE_PERSP2BLACK</b> - Image with transformation matrix with black key color and doubled width.
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* * <b>LAYERMODE_PERSP2WHITE</b> - Image with transformation matrix with white key color and doubled width.
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*
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* <h3>Shared overlay modes</h3>
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*
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* Layer modes can only be combined together if they use the same program. CPP is the minimum required number of SMx clock
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* cycles per pixel.
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* | |PROG_BASE |PROG_KEY |PROG_BLACK |PROG_WHITE |PROG_MONO |PROG_RLE |CPP |
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* |----------------------------|:---------:|:---------:|:---------:|:---------:|:---------:|:---------:|:-----:|
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* |LAYERMODE_BASE | X | | | | | | 2 |
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* |LAYERMODE_KEY | | X | | | | | 6 |
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* |LAYERMODE_BLACK | | | X | | | | 4 |
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* |LAYERMODE_WHITE | | | | X | | | 4 |
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* |LAYERMODE_MONO | | | | | X | | 4 |
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* |LAYERMODE_COLOR | | | | | X | | 2 |
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* |LAYERMODE_RLE | | | | | | X | 3 |
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* |LAYERMODE_SPRITEKEY | | X | | | | | 6 |
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* |LAYERMODE_SPRITEBLACK | | | X | | | | 4 |
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* |LAYERMODE_SPRITEWHITE | | | | X | | | 4 |
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* |LAYERMODE_FASTSPRITEKEY | | X | | | | | 6 |
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* |LAYERMODE_FASTSPRITEBLACK | | | X | | | | 4 |
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* |LAYERMODE_FASTSPRITEWHITE | | | | X | | | 4 |
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* |LAYERMODE_PERSPKEY | | X | | | | | 6 |
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* |LAYERMODE_PERSPBLACK | | | X | | | | 4 |
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* |LAYERMODE_PERSPWHITE | | | | X | | | 4 |
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* |LAYERMODE_PERSP2KEY | | X | | | | | 6 |
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* |LAYERMODE_PERSP2BLACK | | | X | | | | 4 |
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* |LAYERMODE_PERSP2WHITE | | | | X | | | 4 |
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*
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* <h3>Selection of write planes</h3>
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*
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* By default, the image is output from the layers to all output pins. This can be changed by redefining the LayerFirstPin
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* and LayerNumPin fields (in vga_layer.cpp). It is possible to specify for each layer separately which output pins will
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* be written to. This can create a kind of pseudo-transparency. For example, one layer will render curves in red, another
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* layer in green, and the colors will blend independently. When redefining the pins, however, you must take into account
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* that the offset of the pin mapping will shift. The output will always start from the lowest bits of the pixel.
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*
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* <h3>Configure overlay layers</h3>
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*
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* The first step for setting up the overlay layer is to specify the layer mode for the VgaCfg() initialization function.
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* The function detects the required program and the required timing. It does not check if the correct layer modes are
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* combined together.
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*
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* The second step is to initialize the layer descriptor - the sLayer structure in the LayerScreen field. It is convenient
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* to use the LayerSetup() initialization function for this.
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* @{
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*/
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Wayne Venables
