zephr/game: textures, icons, and buttons

- zephr: correctly set cursor when hovering button
- zephr: added texture loading and displaying
- zephr: added icon button
- game: added help and settings icon buttons

texture.c

@@ -0,0 +1,45 @@
+#include "glad/gl.h"
+#include "stb_image.h"
+
+#include "core.h"
+#include "texture.h"
+
+TextureId load_texture(const char *path) {
+  int width, height, nrChannels;
+  unsigned char *data = stbi_load(path, &width, &height, &nrChannels, STBI_rgb_alpha);
+  GLuint texture_id;
+
+  u32 format = GL_RGBA;
+
+  switch (nrChannels) {
+    case 1:
+      format = GL_RED;
+      break;
+    case 2:
+      format = GL_RG;
+      break;
+    case 3:
+      format = GL_RGB;
+      break;
+    case 4:
+      format = GL_RGBA;
+      break;
+  }
+
+  glGenTextures(1, &texture_id);
+  glBindTexture(GL_TEXTURE_2D, texture_id);
+
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+
+  glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
+
+  glGenerateMipmap(GL_TEXTURE_2D);
+
+  stbi_image_free(data);
+
+  return texture_id;
+}