From bac7618df20c3aa05ecfcd19368e7e4f98feddef Mon Sep 17 00:00:00 2001
From: Zack Buhman <zack@buhman.org>
Date: Tue, 5 Dec 2023 21:53:04 +0800
Subject: [PATCH] two triangles

---
 main.cpp  |  2 +-
 scene.cpp | 32 +++++++++++++++++++++-----------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/main.cpp b/main.cpp
index 43cd040..4dc3f3d 100644
--- a/main.cpp
+++ b/main.cpp
@@ -53,7 +53,7 @@ void serial_string(const char * s)
 /* must be aligned to 32-bytes for DMA transfer */
 // the aligned(32) attribute does not actually align to 32 bytes; gcc is the best compiler.
 // `+ 32` to allow for repositioning _scene to an actual 32-byte alignment.
-uint32_t __attribute__((aligned(32))) _scene[((32 * 5) + 32) / 4];
+uint32_t __attribute__((aligned(32))) _scene[((32 * 6) + 32) / 4];
 
 uint32_t * align_32byte(uint32_t * mem)
 {
diff --git a/scene.cpp b/scene.cpp
index 636ed8a..ed642ff 100644
--- a/scene.cpp
+++ b/scene.cpp
@@ -9,10 +9,18 @@
   -0.5,0.5    |  0.5,0.5
  */
 
-float scene_triangle[3][3] = {
-  { 0.f,  -0.5f,  1/10.f},
-  { 0.5f,  0.5f,  1/10.f},
-  { -0.5f,  0.5f,  1/10.f},
+struct triangle {
+  float x;
+  float y;
+  float z;
+  uint32_t color;
+};
+
+const struct triangle scene_triangle[4] = {
+  { -0.5f,   0.5f,  1/10.f, 0x00000000}, // the first two base colors in a
+  { -0.5f,  -0.5f,  1/10.f, 0x00000000}, // triangle strip are ignored
+  {  0.5f,   0.5f,  1/10.f, 0xffff00ff},
+  {  0.5f,  -0.5f,  1/10.f, 0xffffff00},
 };
 
 static float theta = 0;
@@ -25,14 +33,16 @@ uint32_t scene_transform(volatile uint32_t * scene)
   triangle(&scene[(32 * ix) / 4]);
   ix++;
 
-  for (int i = 0; i < 3; i++) {
-    bool end_of_strip = i == 2;
+  for (int i = 0; i < 4; i++) {
+    bool end_of_strip = i == 3;
 
-    float x = scene_triangle[i][0];
-    float y = scene_triangle[i][1];
+    float x = scene_triangle[i].x;
+    float y = scene_triangle[i].y;
+    float x1;
 
-    x = x * __builtin_cosf(theta) - y * __builtin_sinf(theta);
+    x1 = x * __builtin_cosf(theta) - y * __builtin_sinf(theta);
     y = x * __builtin_sinf(theta) + y * __builtin_cosf(theta);
+    x = x1;
     x *= 240.f;
     y *= 240.f;
     x += 320.f;
@@ -41,8 +51,8 @@ uint32_t scene_transform(volatile uint32_t * scene)
     vertex(&scene[(32 * ix) / 4],
            x, // x
            y, // y
-           scene_triangle[i][2], // z
-           0xffff00ff,           // base_color
+           scene_triangle[i].z,     // z
+           scene_triangle[i].color, // base_color
            end_of_strip);
     ix++;
   }