From f4c392ba6ab4fa72222e8d049e60b6baf98493b7 Mon Sep 17 00:00:00 2001 From: jespergravgaard Date: Sun, 4 Apr 2021 09:12:59 +0200 Subject: [PATCH] Better documentation --- src/test/kc/examples/mega65/linedrawing.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/src/test/kc/examples/mega65/linedrawing.c b/src/test/kc/examples/mega65/linedrawing.c index d70d6c2e3..134699985 100644 --- a/src/test/kc/examples/mega65/linedrawing.c +++ b/src/test/kc/examples/mega65/linedrawing.c @@ -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;