Add standalone render context module

include/display/render/context.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define RGB565(R, G, B) \
+    ((uint16_t)((((uint16_t)(R) & 0xF8u) << 8) | \
+                (((uint16_t)(G) & 0xFCu) << 3) | \
+                (((uint16_t)(B) & 0xF8u) >> 3)))
+
+#define BSWAP16(X) \
+    ((uint16_t)((((uint16_t)(X) & 0x00FFu) << 8) | \
+                (((uint16_t)(X) & 0xFF00u) >> 8)))
+
+/* RGB888 -> RGB565 with swapped byte order for ctx->buf */
+#define RGB16(R, G, B) BSWAP16(RGB565((R), (G), (B)))
+
+typedef struct
+{
+    uint16_t* buf;
+    uint16_t width;
+    uint16_t height;
+    uint16_t clip_x0;
+    uint16_t clip_y0;
+    uint16_t clip_x1;
+    uint16_t clip_y1;
+} render_ctx_t;
+
+void render_begin(render_ctx_t* ctx, uint16_t* buf, uint16_t width, uint16_t height);
+void render_set_clip(render_ctx_t* ctx, uint16_t x, uint16_t y, uint16_t width, uint16_t height);
+void render_reset_clip(render_ctx_t* ctx);
+void render_clear(render_ctx_t* ctx, uint16_t color);
+void render_pixel(render_ctx_t* ctx, int x, int y, uint16_t color);
+
+#ifdef __cplusplus
+}
+#endif

src/render/context.c

@@ -0,0 +1,89 @@
+#include "display/render/context.h"
+#include <stdbool.h>
+
+static inline bool in_clip(const render_ctx_t* ctx, int x, int y)
+{
+    return x >= (int)ctx->clip_x0 &&
+           x <= (int)ctx->clip_x1 &&
+           y >= (int)ctx->clip_y0 &&
+           y <= (int)ctx->clip_y1;
+}
+
+void render_begin(render_ctx_t* ctx, uint16_t* buf, uint16_t width, uint16_t height)
+{
+    ctx->buf = buf;
+    ctx->width = width;
+    ctx->height = height;
+    render_reset_clip(ctx);
+}
+
+void render_set_clip(render_ctx_t* ctx, uint16_t x, uint16_t y, uint16_t width, uint16_t height)
+{
+    if (ctx->width == 0 || ctx->height == 0 || width == 0 || height == 0)
+    {
+        ctx->clip_x0 = 0;
+        ctx->clip_y0 = 0;
+        ctx->clip_x1 = 0;
+        ctx->clip_y1 = 0;
+        return;
+    }
+
+    uint32_t x1 = (uint32_t)x + (uint32_t)width - 1u;
+    uint32_t y1 = (uint32_t)y + (uint32_t)height - 1u;
+
+    if (x >= ctx->width || y >= ctx->height)
+    {
+        ctx->clip_x0 = 0;
+        ctx->clip_y0 = 0;
+        ctx->clip_x1 = 0;
+        ctx->clip_y1 = 0;
+        return;
+    }
+
+    if (x1 >= ctx->width)
+        x1 = (uint32_t)ctx->width - 1u;
+    if (y1 >= ctx->height)
+        y1 = (uint32_t)ctx->height - 1u;
+
+    ctx->clip_x0 = x;
+    ctx->clip_y0 = y;
+    ctx->clip_x1 = (uint16_t)x1;
+    ctx->clip_y1 = (uint16_t)y1;
+}
+
+void render_reset_clip(render_ctx_t* ctx)
+{
+    if (ctx->width == 0 || ctx->height == 0)
+    {
+        ctx->clip_x0 = 0;
+        ctx->clip_y0 = 0;
+        ctx->clip_x1 = 0;
+        ctx->clip_y1 = 0;
+        return;
+    }
+
+    ctx->clip_x0 = 0;
+    ctx->clip_y0 = 0;
+    ctx->clip_x1 = (uint16_t)(ctx->width - 1u);
+    ctx->clip_y1 = (uint16_t)(ctx->height - 1u);
+}
+
+void render_clear(render_ctx_t* ctx, uint16_t color)
+{
+    size_t total = (size_t)ctx->width * (size_t)ctx->height;
+    for (size_t i = 0; i < total; ++i)
+    {
+        ctx->buf[i] = color;
+    }
+}
+
+void render_pixel(render_ctx_t* ctx, int x, int y, uint16_t color)
+{
+    if (x < 0 || y < 0 || x >= (int)ctx->width || y >= (int)ctx->height)
+        return;
+
+    if (!in_clip(ctx, x, y))
+        return;
+
+    ctx->buf[(size_t)y * ctx->width + (size_t)x] = color;
+}