r61524: add a r61524_display_rect() function for small regions

include/gint/drivers/r61524.h

@@ -35,16 +35,33 @@ enum {
    @method  Transfer method, see above */
 void r61524_display(uint16_t *vram, int start, int height, int method);
 
+/* r61524_display_rect(): Send a rectangular section of VRAM to the display
+
+   This function updates the rectangle going from (xmin,ymin) to (xmax,ymax) in
+   the VRAM to the display (both ends included). This can be faster than a full
+   dupdate() or a striped r61524_display() depending on the situation. However,
+   because the source VRAM is not contiguous, the transfer is only possible by
+   CPU, so this is only interesting for small regions.
+
+   @vram        Source VRAM with a stride of 396*2 bytes
+   @xmin @xmax  Horizontal range to be updated (both included)
+   @ymin @ymax  Vertical range to be updated (both included) */
+void r61524_display_rect(uint16_t *vram, int xmin, int xmax, int ymin,
+   int ymax);
+
 /* r61524_start_frame(): Prepare the display for a region update
 
    This function sets up the display driver to receive graphics data to update
-   liens [start] to [start+height-1] (both included) of the current window.
+   the rectangle going from (xmin,ymin) to (xmax,ymax) (both included). This is
-   This is the initial step of r61524_display(), which is normally followed by
+   the initial step of r61524_display(), which is normally followed by writing
-   writing all the data to 0xb4000000.
+   all the data to 0xb4000000.
+
+   In order to write with the DMA, it is necessary to write the full horizontal
+   range and select ymin and ymax to be congruent to 0 and 3 modulo 4.
 
    This function can be used to implement additional display driver update
    methods or alternate rendering pipelines. */
-void r61524_start_frame(int start, int height);
+void r61524_start_frame(int xmin, int xmax, int ymin, int ymax);
 
 /* r162524_win_get() and r61524_win_set(): Manipulate the display window
 

src/r61524/r61524.c

@@ -134,10 +134,10 @@ void r61524_win_set(uint16_t HSA, uint16_t HEA, uint16_t VSA, uint16_t VEA)
 
 /* TODO: r61524: update, backlight, brightness, gamma */
 
-void r61524_start_frame(int start, int height)
+void r61524_start_frame(int xmin, int xmax, int ymin, int ymax)
 {
 	/* Move the window to the desired region, then select address 0 */
-	r61524_win_set(0, 395, start, start + height - 1);
+	r61524_win_set(xmin, xmax, ymin, ymax);
 	select(ram_address_horizontal);
 	write(0);
 	select(ram_address_vertical);
@@ -153,7 +153,7 @@ void r61524_display(uint16_t *vram, int start, int height, int method)
 	   the DMA might write data *while* we're sending commands! */
 	dma_transfer_wait(0);
 
-	r61524_start_frame(start, height);
+	r61524_start_frame(0, 395, start, start + height - 1);
 
 	if(method == R61524_CPU)
 	{
@@ -181,6 +181,21 @@ void r61524_display(uint16_t *vram, int start, int height, int method)
 	}
 }
 
+void r61524_display_rect(uint16_t *vram, int xmin, int xmax, int ymin,
+	int ymax)
+{
+	dma_transfer_wait(0);
+	r61524_start_frame(xmin, xmax, ymin, xmax);
+
+	vram += 396 * ymin + xmin;
+
+	for(int y = 0; y < ymax - ymin + 1; y++) {
+		for(int x = 0; x < xmax - xmin + 1; x++)
+			write(vram[x]);
+		vram += 396;
+	}
+}
+
 //---
 // State and driver metadata
 //---