FasTC/PVRTCEncoder/src/Block.h
Pavel Krajcevski 1115c2f9e4 Add 2BPP helper functions for our blocks.
Namely, there are two things that we need to do:
1. Figure out the sub-mode based on the mode bit and the structure of the modulation data. The comments in Block.h describe how we do this.
2. For a given texel index, return 2BPP texel modulation bits.
2013-09-12 14:30:08 -04:00

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/* FasTC
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* Pavel Krajcevski
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#ifndef PVRTCENCODER_SRC_BLOCK_H_
#define PVRTCENCODER_SRC_BLOCK_H_
#include "Core/include/TexCompTypes.h"
#include "Pixel.h"
namespace PVRTCC {
class Block {
public:
explicit Block(const uint8 *data);
Pixel GetColorA();
Pixel GetColorB();
bool GetModeBit() const {
return static_cast<bool>((m_LongData >> 32) & 0x1);
}
// For 2BPP PVRTC, if the mode bit is set, then we use the modulation data
// as 2 bits for every other texel in the 8x4 block in a checkerboard pattern.
// The interleaved texel data is decided by averaging nearby texel modulation
// values. There are three different ways to average nearby texels: Either we
// average the neighboring horizontal or vertical pixels using (a + b) / 2, or
// we neighbor all four neighbors using (a + b + c + d + 1) / 4.
enum E2BPPSubMode {
e2BPPSubMode_All,
e2BPPSubMode_Horizontal,
e2BPPSubMode_Vertical
};
// For 2BPP PVRTC, this function determines the submode of the given block. The
// submode is determined by first checking the first 2bit texel index. This texel
// uses the high bit as a 1 bit modulation value (i.e. chooses colors A or B) and
// the low bit is used to determine the sub-mode. If the low bit is 0, then we
// will use e2BPPSubMode_All as defined above. If the low bit is 1, then we must
// look at the center texel (index 10) to determine the sub-mode. In this case,
// we treat the center texel as 1 bit modulation as well, and we use the low bit to
// determine the sub-mode where 0 is e2BPPSubMode_Horizontal and 1 is
// e2BPPSubMode_Vertical
E2BPPSubMode Get2BPPSubMode() const;
// Returns the modulation value for the texel in the 4x4 block. The texels are
// numbered as follows:
// 0 1 2 3
// 4 5 6 7
// 8 9 10 11
// 12 13 14 15
uint8 GetLerpValue(uint32 texelIdx) const;
// This returns the modulation value for the texel in the block interpreted as
// 2BPP. If the modulation bit is not set, then it expects a number from 0-31
// and does the same operation as GetLerpValue. If the modulation bit is set,
// then this function expects a number from 0-15 and returns the corresponding
// modulation bits given the sub-mode. Note, this function does not do the
// averaging described for E2BPPSubMode because this averaging relies on
// global information.
uint8 Get2BPPLerpValue(uint32 texelIdx) const;
private:
union {
uint8 m_ByteData[8];
uint64 m_LongData;
};
bool m_ColorACached;
Pixel m_ColorA;
bool m_ColorBCached;
Pixel m_ColorB;
};
} // namespace PVRTCC
#endif // PVRTCENCODER_SRC_BLOCK_H_