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BbcScreen.cpp
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BbcScreen.cpp
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/*
* Copyright © 1999-2000 David Robinson
* Copyright © 2007-2016 Matt Robinson
*
* SPDX-License-Identifier: GPL-3.0-or-later
*/
#include <cstring>
#include <stdexcept>
#include "BbcScreen.h"
const int BLOCK_BYTES = 8; // Number bytes in a block
const int WIDTH0 = 640; // Width of BBC MODE 0 screen
const int WIDTH14 = 320; // Width of BBC MODE 1 & 4 screens
const int WIDTH25 = 160; // Width of BBC MODE 2 & 5 screens
const int XBLKS012 = 80; // Horizontal blocks in MODE 0, 1 & 2 screens
const int XBLKS45 = 40; // Horizontal blocks in MODE 4 & 5 screens
void BbcScreen::init(int screenMemSize)
{
if(screenMemSize > MAX_MEMSIZE)
{
throw std::invalid_argument("Requested screen memory size too large");
}
screenMemSize_ = screenMemSize;
setMode(mode_);
}
BbcScreen::BbcScreen(int screenMemSize)
{
init(screenMemSize);
// Initialise the screen memory to all zeros (to match BBC)
for(int init = 0; init < screenMemSize; init++)
{
screenStorage_[init] = 0;
}
}
BbcScreen::BbcScreen(int screenMemSize, uint8_t *screenData)
{
init(screenMemSize);
memcpy(screenStorage_, screenData, screenMemSize);
}
void BbcScreen::setMode(uint8_t mode)
{
mode = mode % 8;
if(mode == 3 || mode == 6 || mode == 7)
{
throw std::invalid_argument("modes 3, 6 and 7 are not supported");
}
mode_ = mode;
int blocksInFile = screenMemSize_ / BLOCK_BYTES;
switch(mode_)
{
case 0:
screenWidth_ = WIDTH0;
blockRows_ = blocksInFile / XBLKS012;
break;
case 1:
screenWidth_ = WIDTH14;
blockRows_ = blocksInFile / XBLKS012;
break;
case 2:
screenWidth_ = WIDTH25;
blockRows_ = blocksInFile / XBLKS012;
break;
case 4:
screenWidth_ = WIDTH14;
blockRows_ = blocksInFile / XBLKS45;
break;
case 5:
screenWidth_ = WIDTH25;
blockRows_ = blocksInFile / XBLKS45;
break;
}
if(blockRows_ == 0) {
// The screen memory doesn't have even one row of blocks
throw std::runtime_error("Allocated screen too small");
}
// Calculate how tall the image is based on the number of rows of blocks.
screenHeight_ = blockRows_ * BLOCK_BYTES;
// Set the default colour mappings for the mode
switch(mode)
{
case 0:
case 4:
palette_[0] = 0;
palette_[1] = 7;
break;
case 1:
case 5:
palette_[0] = 0;
palette_[1] = 1;
palette_[2] = 3;
palette_[3] = 7;
break;
case 2:
for(uint8_t i = 0; i < PALETTE_SIZE; i++)
{
palette_[i] = i;
}
break;
}
}
uint8_t BbcScreen::getMode()
{
return mode_;
}
void BbcScreen::setScreenByte(int address, uint8_t byte)
{
if(address >= screenMemSize_)
{
throw std::invalid_argument("address out of bounds");
}
screenStorage_[address] = byte;
}
uint8_t BbcScreen::getScreenByte(int address)
{
if(address >= screenMemSize_)
{
throw std::invalid_argument("address out of bounds");
}
return screenStorage_[address];
}
int BbcScreen::getScreenWidth()
{
return screenWidth_;
}
int BbcScreen::getScreenHeight()
{
return screenHeight_;
}
void BbcScreen::setColour(uint8_t colour, uint8_t value)
{
if(colour >= PALETTE_SIZE)
{
throw std::invalid_argument("Colour out of range");
}
if(value >= PALETTE_SIZE)
{
throw std::invalid_argument("Value out of range");
}
palette_[colour] = value;
}
uint8_t BbcScreen::getColour(uint8_t colour)
{
if(colour >= PALETTE_SIZE)
{
throw std::invalid_argument("Colour out of range");
}
return palette_[colour];
}
void BbcScreen::draw(DrawPixel callback)
{
switch(mode_)
{
case 0:
case 4:
draw04(callback);
break;
case 1:
case 5:
draw15(callback);
break;
case 2:
draw2(callback);
break;
}
}
// MODE 0 or MODE 4 picture
void BbcScreen::draw04(DrawPixel callback)
{
int bit, i, j, k;
uint8_t thisByte;
uint8_t index;
int nX = 0;
int nY = 0;
int nBlocks = XBLKS012;
if(mode_ == 4) {
nBlocks = XBLKS45;
}
int address = 0;
for(k = 0; k < blockRows_; k++)
{
for(j = 0; j < nBlocks; j++)
{
for(i = 0; i < BLOCK_BYTES; i++)
{
thisByte = screenStorage_[address];
for(bit = 0; bit < 8; bit++)
{
index = thisByte & 1;
callback((nX+7)-bit, nY+i, getColour(index));
thisByte = thisByte >> 1;
}
address++;
}
nX = nX + 8;
}
nX = 0;
nY = nY + 8;
}
}
// MODE 1 or MODE 5 picture
void BbcScreen::draw15(DrawPixel callback)
{
int i, j, k;
uint8_t thisByte;
uint8_t index;
int nX = 0;
int nY = 0;
int nBlocks = XBLKS012;
if(mode_ == 5) {
nBlocks = XBLKS45;
}
int address = 0;
for(k = 0; k < blockRows_; k++)
{
for(j = 0; j < nBlocks; j++)
{
for(i = 0; i < BLOCK_BYTES; i++)
{
thisByte = screenStorage_[address];
index = ((thisByte >> 6) & 2) | ((thisByte >> 3) & 1);
callback(nX, nY+i, getColour(index));
index = ((thisByte >> 5) & 2) | ((thisByte >> 2) & 1);
callback(nX+1, nY+i, getColour(index));
index = ((thisByte >> 4) & 2) | ((thisByte >> 1) & 1);
callback(nX+2, nY+i, getColour(index));
index = ((thisByte >> 3) & 2) | (thisByte & 1);
callback(nX+3, nY+i, getColour(index));
address++;
}
nX = nX + 4;
}
nX = 0;
nY = nY + 8;
}
}
// MODE 2 picture
void BbcScreen::draw2(DrawPixel callback)
{
int i, j, k;
uint8_t thisByte;
uint8_t index;
int nX = 0;
int nY = 0;
int address = 0;
for(k = 0; k < blockRows_; k++) {
for(j = 0; j < XBLKS012; j++) {
for(i = 0; i < BLOCK_BYTES; i++) {
thisByte = screenStorage_[address];
index = ((thisByte >> 4) & 8) | ((thisByte >> 3) & 4) | ((thisByte >> 2) & 2) | ((thisByte >> 1) & 1);
callback(nX, nY+i, getColour(index));
index = ((thisByte >> 3) & 8) | ((thisByte >> 2) & 4) | ((thisByte >> 1) & 2) | (thisByte & 1);
callback(nX+1, nY+i, getColour(index));
address++;
}
nX = nX + 2;
}
nX = 0;
nY = nY + 8;
}
}