examples: add triangle_rotating example

Author: buhman

Makefile

@@ -10,17 +10,10 @@ arm9/%.bin: phony
 arm7/%.bin: phony
 	make -C arm7/ $(notdir $@)
 
-OBJ = \
-	header.o \
-	arm9/arm9.bin.o \
-	arm7/arm7.bin.o
-cartridge.elf: $(OBJ)
-
-TRIANGLE_OBJ = \
-	header.o \
-	arm9/triangle.bin.o \
-	arm7/arm7.bin.o
-triangle.elf: $(TRIANGLE_OBJ)
+DEFAULT = header.o arm7/arm7.bin.o
+
+triangle.elf: $(DEFAULT) arm9/triangle.bin.o
+triangle_rotating.elf: $(DEFAULT) arm9/triangle_rotating.bin.o
 
 TARGET = arm-none-eabi-
 AARCH = -march=armv4t -mlittle-endian

arm9/Makefile

@@ -16,10 +16,11 @@ OBJ = \
 
 arm9.elf: $(OBJ)
 
-foo = start.o examples/triangle.o
-triangle.elf: $(foo)
+triangle.elf: start.o examples/triangle.o
 
-CFLAGS += -I../include
+triangle_rotating.elf: start.o examples/triangle_rotating.o ../math/cos_table_fp12.o ../math/cos.o
+
+CFLAGS += -I../include -I../math
 
 include arm9.mk
 include ../common.mk

arm9/examples/triangle_rotating.c

@@ -0,0 +1,175 @@
+#include "io_registers.h"
+#include "bits.h"
+
+#include "math.h"
+
+void main()
+{
+  // power control
+  io_registers.a.POWCNT = 0
+    | POWCNT__lcd_output_destination__a_to_upper__b_to_lower
+    | POWCNT__geometry_engine__enable
+    | POWCNT__rendering_engine__enable
+    | POWCNT__lcd__enable;
+
+  // enable bg0 and 3d graphics
+  io_registers.a.DISPCNT = 0
+    | DISPCNT__display_mode__graphics_display
+    | DISPCNT__bg0__enable
+    | DISPCNT__display_selection_for_bg0__3d_graphics
+    ;
+
+  // clear matrix stack status
+  io_registers.a.GXSTAT |= GXSTAT__matrix_stack_status__overflow_or_underflow;
+
+  // load identity matrices
+  io_registers.a.MTX_MODE = MTX_MODE__matrix_mode__projection;
+  io_registers.a.MTX_IDENTITY = 0;
+
+  io_registers.a.MTX_MODE = MTX_MODE__matrix_mode__position;
+  io_registers.a.MTX_IDENTITY = 0;
+
+  io_registers.a.MTX_MODE = MTX_MODE__matrix_mode__position_and_vector;
+  io_registers.a.MTX_IDENTITY = 0;
+
+  // disable all 3d effects
+  io_registers.a.DISP3DCNT = 0
+    | DISP3DCNT__clear_image__disable
+    | DISP3DCNT__fog_master__disable
+    | DISP3DCNT__edge_marking__disable
+    | DISP3DCNT__anti_aliasing__disable
+    | DISP3DCNT__alpha_blending__disable
+    | DISP3DCNT__alpha_test__disable
+    | DISP3DCNT__texture_mapping__disable;
+
+  // set the 3d clear color to a dark red
+  io_registers.a.CLEAR_COLOR = 0
+    | CLEAR_COLOR__clear_polygon_id(31)
+    | CLEAR_COLOR__alpha_value(31)
+    | CLEAR_COLOR__blue(1)
+    | CLEAR_COLOR__green(1)
+    | CLEAR_COLOR__red(10);
+
+  // set the depth buffer clear value to the maximum value
+  io_registers.a.CLEAR_DEPTH = CLEAR_DEPTH__value(0x7fff);
+
+  // the following polygons are fully opaque and are not
+  // backface-culled
+  io_registers.a.POLYGON_ATTR = 0
+    | POLYGON_ATTR__alpha_value(31)
+    | POLYGON_ATTR__render_front_surface__enable
+    | POLYGON_ATTR__render_back_surface__enable;
+
+  // the 3d viewport is the entire display area
+  io_registers.a.VIEWPORT = 0
+    | VIEWPORT__y2(191)
+    | VIEWPORT__x2(255)
+    | VIEWPORT__y1(0)
+    | VIEWPORT__x1(0);
+
+  // VTX_10 uses signed 4.6 floating point (10 bit)
+  // | 9 | 8 7 6 | 5 4 3 2 1 0 |
+  // | s |  int  | decimal     |
+  int fixed_point_divisor = 64; // == 2⁶
+
+  // equilateral triangle; centered around the display origin in NDC
+  /*
+        A
+       / \
+      B---C
+
+   */
+
+  // fixed point constants; these are converted from floating-point to
+  // integer at compile-time
+  int ax =  0.0           * fixed_point_divisor;
+  int ay =  1.0           * fixed_point_divisor;
+
+  int bx = -0.86602540378 * fixed_point_divisor; // - sqrt(3) / 2
+  int by = -0.5           * fixed_point_divisor;
+
+  int cx =  0.86602540378 * fixed_point_divisor; // + sqrt(3) / 2
+  int cy = -0.5           * fixed_point_divisor;
+
+  int  z =  1.0           * fixed_point_divisor;
+
+  // degrees
+  int theta = 0;
+
+  while (1) {
+    // calculate sin/cos for 2d rotation; signed fp20.12 result
+    int cos = cos_fp12(theta);
+    int sin = sin_fp12(theta);
+
+    // load this 4x3 rotation matrix:
+    //
+    // | cos(θ)  -sin(θ)     0 |
+    // | sin(θ)   cos(θ)     0 |
+    // |     0        0      1 |
+    // |     0        0      0 |
+    //
+    // the 4x3 matrix load order is:
+    //
+    // | 0 1 2 |
+    // | 3 4 5 |
+    // | 6 7 8 |
+    // | 9 a b |
+
+    io_registers.a.MTX_MODE = MTX_MODE__matrix_mode__position;
+    io_registers.a.MTX_LOAD_4X3 = cos;     // 0
+    io_registers.a.MTX_LOAD_4X3 = -sin;    // 1
+    io_registers.a.MTX_LOAD_4X3 = 0;       // 2
+
+    io_registers.a.MTX_LOAD_4X3 = sin;     // 3
+    io_registers.a.MTX_LOAD_4X3 = cos;     // 4
+    io_registers.a.MTX_LOAD_4X3 = 0;       // 5
+
+    io_registers.a.MTX_LOAD_4X3 = 0;       // 6
+    io_registers.a.MTX_LOAD_4X3 = 0;       // 7
+    io_registers.a.MTX_LOAD_4X3 = 1 << 12; // 8
+
+    io_registers.a.MTX_LOAD_4X3 = 0;       // 9
+    io_registers.a.MTX_LOAD_4X3 = 0;       // a
+    io_registers.a.MTX_LOAD_4X3 = 0;       // b
+
+    // the following vertices are a triangle
+    io_registers.a.BEGIN_VTXS = BEGIN_VTXS__type__triangle;
+
+    io_registers.a.COLOR = COLOR__blue(31);
+    io_registers.a.VTX_10 = 0
+      | VTX_10__z_coordinate(z)
+      | VTX_10__y_coordinate(ay)
+      | VTX_10__x_coordinate(ax);
+
+    io_registers.a.COLOR = COLOR__green(31);
+    io_registers.a.VTX_10 = 0
+      | VTX_10__z_coordinate(z)
+      | VTX_10__y_coordinate(by)
+      | VTX_10__x_coordinate(bx);
+
+    io_registers.a.COLOR = COLOR__red(31);
+    io_registers.a.VTX_10 = 0
+      | VTX_10__z_coordinate(z)
+      | VTX_10__y_coordinate(cy)
+      | VTX_10__x_coordinate(cx);
+
+    // end of the triangle
+    io_registers.a.END_VTXS = 0;
+
+    // wait for the geomtry engine
+    while (io_registers.a.GXSTAT & GXSTAT__geometry_engine_busy);
+
+    // wait for the end of the current frame
+    while (io_registers.a.VCOUNT != 262);
+    while (io_registers.a.VCOUNT == 262);
+
+    // swap buffers
+    io_registers.a.SWAP_BUFFERS = 0;
+
+    // increment theta once per frame
+    theta += 1;
+    if (theta >= 360) {
+      theta = 0;
+    }
+  }
+}