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Better documentation

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jespergravgaard 2021-04-04 09:12:59 +02:00
parent 65eb2edc12
commit f4c392ba6a
1 changed files with 9 additions and 6 deletions
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15
src/test/kc/examples/mega65/linedrawing.c
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@ -69,27 +69,30 @@ const char LINE_DMA_COMMAND_SRC_OFFSET = 19;
// Offset of the DMA destination
const char LINE_DMA_COMMAND_DEST_OFFSET = 22;
// Use the DMA to draw a line on a canvas.
// Graphics mode is 1 byte per pixel. Addressing is based on columns of 8px * 200px arranged to have linear addressing.
// The line is based on a major axis and a minor axis. The major axis is incremented by 1 for each dot. The minor axis is incremented or decremented based on the slope.
// - addr: Start address where the first pixel is placed
// - slope: The slope of the minor axis. Unsigned number representing [0;1[
// - count: The length of the line along the major axis
// - colour: The colour of the line
// - is_direction_y: Defines the major axis. 0: X-axis, 1: Y-axis.
// - is_slope_negative: Defines whether the minor axis is incremented or decremented whenever slope>65536. 0: increment 1: decrement.
void line_dma_execute(unsigned long addr, unsigned int slope, unsigned int count, char colour, char is_direction_y, char is_slope_negative) {
// Put slope into DMA options
line_dma_command[LINE_DMA_COMMAND_SLOPE_OFFSET] = LOBYTE(slope);
line_dma_command[LINE_DMA_COMMAND_SLOPE_OFFSET + 2] = HIBYTE(slope);
// Load DMA dest address with the address of the first pixel
line_dma_command[LINE_DMA_COMMAND_DEST_OFFSET + 0] = BYTE0(addr);
line_dma_command[LINE_DMA_COMMAND_DEST_OFFSET + 1] = BYTE1(addr);
line_dma_command[LINE_DMA_COMMAND_DEST_OFFSET + 2] = BYTE2(addr);
// Source is the colour
line_dma_command[LINE_DMA_COMMAND_SRC_OFFSET] = colour;
// Count is number of pixels, i.e., dy.
line_dma_command[LINE_DMA_COMMAND_COUNT_OFFSET] = LOBYTE(count);
line_dma_command[LINE_DMA_COMMAND_COUNT_OFFSET + 1] = HIBYTE(count);
// Line mode active, major axis is Y
line_dma_command[LINE_DMA_COMMAND_MODE_OFFSET] = DMA_OPTION_LINE_MODE_ENABLE + (is_direction_y ? DMA_OPTION_LINE_MODE_DIRECTION_Y : 0x00) + (is_slope_negative ? DMA_OPTION_LINE_MODE_SLOPE_NEGATIVE : 0x00);
// Set address of DMA list
DMA->ADDRMB = 0;
DMA->ADDRBANK = 0;