refactor: transparent render (#14)

* fix(renderer): defer uniform location retrieval and add view matrix in outline rendering

* refactor(gameplay): encapsulate per-type vertex data into VertexData struct

* feat(rendering): separate transparent blocks into discard and blend modes

* feat(renderer): implement order-independent transparency

* fix(shaders): reduce alpha discard threshold to 0.8

assets/shaders/block_composite_f_shader.glsl

@@ -0,0 +1,19 @@
+#version 460
+
+uniform sampler2D u_accumTex;
+uniform sampler2D u_revealTex;
+in vec2 TexCoord;
+out vec4 FragColor;
+
+void main() {
+    vec4 a = texture(u_accumTex, TexCoord);
+    float r = texture(u_revealTex, TexCoord).r;
+
+    if (a.a < 1e-4) discard;
+
+    vec3 color = a.rgb / max(a.a, 1e-5);
+    float transmittance = r;
+    float opacity = 1.0 - transmittance;
+
+    FragColor = vec4(color * opacity, opacity);
+}