Add support for 256 color indexed palette

CMakeLists.txt

@@ -3,6 +3,8 @@ project(vtrenderlib C)
 
 add_library(vtrenderlib STATIC vtrenderlib.c)
 
+target_compile_options(vtrenderlib PRIVATE -Wall -Wextra -Werror)
+
 # Public include directory for consumers
 target_include_directories(vtrenderlib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
 

demos/boids/main.c

@@ -96,7 +96,7 @@ struct vt_boid
     int cur_heading_time;
 
     // rendering data
-    enum vtr_color color;
+    vtr_fgcolor_t color;
     struct vec2f trail[VT_BOID_TRAIL_SIZE];
     size_t trail_idx;
     size_t trail_len;
@@ -241,7 +241,7 @@ static void debug_print(uint16_t row, uint16_t col, const char* fmt, ...)
     va_end(args);
 }
 
-static void debug_vec(struct vec2f origin, struct vec2f vec, float scale, enum vtr_color fgc)
+static void debug_vec(struct vec2f origin, struct vec2f vec, float scale, vtr_fgcolor_t fgc)
 {
     struct vtr_vertex start = vec2f_project(origin);
     struct vtr_vertex end = vec2f_project(vec2f_mul_add(origin, vec, scale));

vtrenderlib.c

@@ -18,8 +18,8 @@
 // - VT/xterm escape sequences work in the same manner:
 //   1. Shell/app: 0x1B 0x5B 0x33 0x31 0x6D   # ESC [ 3 1 m  → “set foreground color to red” -> written to PTY slave via STDOUT_FILENO
 //   2. Kernel PTY layer: handles line discipline, raw mode (bytes pass through unchanged) vs canonical mode (control chars handled),
-//      forwards data to PTY slave.
-//   3. Terminal emulator: reads data from PTY slave, recognizes `ESC [ 31 m`, changes rendering color, paints to the screen.
+//      forwards data to PTY master.
+//   3. Terminal emulator: reads data from PTY master, recognizes `ESC [ 31 m`, changes rendering color, paints to the screen.
 //
 
 //
@@ -261,7 +261,7 @@ struct vtr_canvas* vtr_canvas_create(int ttyfd)
 static int sendseq(int ttyfd, const char* seq, size_t nbytes)
 {
     ssize_t res = write(ttyfd, seq, nbytes);
-    if (res == -1 || res != nbytes) {
+    if (res == -1 || (size_t)res != nbytes) {
         return -1;
     }
 
@@ -406,7 +406,7 @@ static size_t set_pos_s(char* seq, size_t seqcap, uint16_t row, uint16_t col)
     return nwritten;
 }
 
-static size_t draw_cell_s(char* seq, size_t seqcap, uint8_t mask)
+static size_t draw_cell_s(char* seq, __attribute__((unused)) size_t seqcap, uint8_t mask)
 {
     assert(seqcap >= 3);
 
@@ -417,21 +417,46 @@ static size_t draw_cell_s(char* seq, size_t seqcap, uint8_t mask)
     return 3;
 }
 
-static size_t set_foreground_color_s(char* seq, size_t seqcap, uint8_t fgc)
+static size_t u8_to_dec(char* dst, uint8_t v)
+{
+    if (v >= 100) {
+        dst[0] = '0' + v / 100;
+        dst[1] = '0' + (v / 10) % 10;
+        dst[2] = '0' + v % 10;
+        return 3;
+    }
+    if (v >= 10) {
+        dst[0] = '0' + v / 10;
+        dst[1] = '0' + v % 10;
+        return 2;
+    }
+    dst[0] = '0' + v;
+    return 1;
+}
+
+static size_t set_foreground_color_s(char* seq, __attribute__((unused)) size_t seqcap, uint8_t fgc)
 {
-    assert(fgc >= VTR_COLOR_DEFAULT && fgc < VTR_COLOR_TOTAL);
     assert(seqcap >= 5);
 
     seq[0] = 0x1b;
     seq[1] = '[';
     seq[2] = '3';
-    seq[3] = (fgc == VTR_COLOR_DEFAULT ? '9' : '0' + fgc - 1);
-    seq[4] = 'm';
-
-    return 5;
+    if (fgc < VTR_COLOR_SGR8_TOTAL) {
+        seq[3] = (fgc == VTR_COLOR_DEFAULT ? '9' : '0' + fgc - 1);
+        seq[4] = 'm';
+        return 5;
+    }
+    assert(seqcap >= 11);
+    seq[3] = '8';
+    seq[4] = ';';
+    seq[5] = '5';
+    seq[6] = ';';
+    size_t n = u8_to_dec(&seq[7], fgc - 1);
+    seq[7 + n] = 'm';
+    return 8 + n;
 }
 
-static size_t put_char_s(char* seq, size_t seqcap, char chr)
+static size_t put_char_s(char* seq, __attribute__((unused)) size_t seqcap, char chr)
 {
     assert(seqcap >= 1);
     seq[0] = chr;
@@ -517,7 +542,7 @@ int vtr_swap_buffers(struct vtr_canvas* vt)
     return sendseq(vt->fd, vt->seqlist, seqlen);
 }
 
-static void render_dot(struct vtr_stencil_buf* sb, uint16_t x, uint16_t y, enum vtr_color fgc)
+static void render_dot(struct vtr_stencil_buf* sb, uint16_t x, uint16_t y, vtr_fgcolor_t fgc)
 {
     assert(x < sb->xdots && y < sb->ydots);
 
@@ -546,7 +571,7 @@ void vtr_render_dot(struct vtr_canvas* vt, int x, int y)
     vtr_render_dotc(vt, x, y, VTR_COLOR_DEFAULT);
 }
 
-void vtr_render_dotc(struct vtr_canvas* vt, int x, int y, enum vtr_color fgc)
+void vtr_render_dotc(struct vtr_canvas* vt, int x, int y, vtr_fgcolor_t fgc)
 {
     if (point_test(vt, x, y)) {
         render_dot(vt->cur_sb, x, y, fgc);
@@ -562,12 +587,12 @@ static float calc_slope(uint32_t x0, uint32_t y0, uint32_t x1, uint32_t y1)
     return (x1 == x0 ? INFINITY : ((float)y1 - y0) / ((float)x1 - x0));
 }
 
-static void scan_line(struct vtr_stencil_buf* sb, uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, enum vtr_color fgc)
+static void scan_line(struct vtr_stencil_buf* sb, uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, vtr_fgcolor_t fgc)
 {
-    assert(x0 >= 0 && x0 < sb->xdots);
-    assert(x1 >= 0 && x1 < sb->xdots);
-    assert(y0 >= 0 && y0 < sb->ydots);
-    assert(y1 >= 0 && y1 < sb->ydots);
+    assert(x0 < sb->xdots);
+    assert(x1 < sb->xdots);
+    assert(y0 < sb->ydots);
+    assert(y1 < sb->ydots);
 
     float m = calc_slope(x0, y0, x1, y1);
     int hdir = (x0 < x1 ? 1 : -1);
@@ -637,7 +662,7 @@ void vtr_scan_line(struct vtr_canvas* vt, int x0, int y0, int x1, int y1)
     vtr_scan_linec(vt, x0, y0, x1, y1, VTR_COLOR_DEFAULT);
 }
 
-void vtr_scan_linec(struct vtr_canvas* vt, int x0, int y0, int x1, int y1, enum vtr_color fgc)
+void vtr_scan_linec(struct vtr_canvas* vt, int x0, int y0, int x1, int y1, vtr_fgcolor_t fgc)
 {
     int dx = x1 - x0, dy = y1 - y0;
     int xmin = 0, ymin = 0;
@@ -688,7 +713,7 @@ int vtr_trace_poly(struct vtr_canvas* vt, size_t nvertices, const struct vtr_ver
     return vtr_trace_polyc(vt, nvertices, vlist, VTR_COLOR_DEFAULT);
 }
 
-int vtr_trace_polyc(struct vtr_canvas* vt, size_t nvertices, const struct vtr_vertex* vlist, enum vtr_color fgc)
+int vtr_trace_polyc(struct vtr_canvas* vt, size_t nvertices, const struct vtr_vertex* vlist, vtr_fgcolor_t fgc)
 {
     assert(vt);
     assert(vlist);
@@ -761,7 +786,9 @@ int vtr_trace_polyc(struct vtr_canvas* vt, size_t nvertices, const struct vtr_ve
                 // Intercepts can repeat if 2 edges meet at current y, ignore that
                 switch(ncepts) {
                     case 2: if (xcepts[1] == xcept) continue;
+                            /* fallthrough */
                     case 1: if (xcepts[0] == xcept) continue;
+                            /* fallthrough */
                     case 0: break;
                 }
 

vtrenderlib.h

@@ -77,27 +77,38 @@ enum vtr_color
     VTR_COLOR_CYAN,
     VTR_COLOR_WHITE,
 
-    VTR_COLOR_TOTAL // always last
+    VTR_COLOR_SGR8_TOTAL // always last
 };
 
+/*
+ * Foreground color type. Accepts enum vtr_color or VTR_COLOR256(idx) values.
+ */
+typedef uint8_t vtr_fgcolor_t;
+
+/*
+ * 256-color palette (ITU-T T.416 / ISO/IEC 8613-6).
+ * Index 255 (light grey) is mapped to VTR_COLOR_WHITE since 0 is reserved for VTR_COLOR_DEFAULT.
+ */
+#define VTR_COLOR256(_idx)  ((vtr_fgcolor_t)((_idx) >= 255 ? VTR_COLOR_WHITE : (_idx) + 1))
+
 /**
  * Render a dot at given VT coordinates.
  */
 void vtr_render_dot(struct vtr_canvas* vt, int x, int y);
-void vtr_render_dotc(struct vtr_canvas* vt, int x, int y, enum vtr_color fgc);
+void vtr_render_dotc(struct vtr_canvas* vt, int x, int y, vtr_fgcolor_t fgc);
 
 /**
  * Scan a line given two dot coordinates.
  */
 void vtr_scan_line(struct vtr_canvas* vt, int x0, int y0, int x1, int y1);
-void vtr_scan_linec(struct vtr_canvas* vt, int x0, int y0, int x1, int y1, enum vtr_color fgc);
+void vtr_scan_linec(struct vtr_canvas* vt, int x0, int y0, int x1, int y1, vtr_fgcolor_t fgc);
 
 /**
  * Trace a polygon path given a list of vertices.
  * The last vertex is traced back to the first one and the resulting polygon filled.
  */
 int vtr_trace_poly(struct vtr_canvas* vt, size_t nvertices, const struct vtr_vertex* vertexlist);
-int vtr_trace_polyc(struct vtr_canvas* vt, size_t nvertices, const struct vtr_vertex* vertexlist, enum vtr_color fgc);
+int vtr_trace_polyc(struct vtr_canvas* vt, size_t nvertices, const struct vtr_vertex* vertexlist, vtr_fgcolor_t fgc);
 
 /**
  * Print some text at the specified location.