From af89079d62b48bbf3c9ca9492c235c0894100d4f Mon Sep 17 00:00:00 2001
From: allem <allemang.d@gmail.com>
Date: Mon, 15 Jul 2019 23:07:51 -0400
Subject: [PATCH] simple cyan triangle

---
 cosets/src/main.cpp | 54 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 46 insertions(+), 8 deletions(-)

diff --git a/cosets/src/main.cpp b/cosets/src/main.cpp
index 0da7e0a..e807fe6 100644
--- a/cosets/src/main.cpp
+++ b/cosets/src/main.cpp
@@ -62,6 +62,7 @@ public:
 
 class CosetsWindow : public Window {
    GLint program;
+   GLuint vao;
 
    GLint build_shader(GLenum type, const string &name, const string &src) {
       const char *c_str = src.c_str();
@@ -78,36 +79,73 @@ class CosetsWindow : public Window {
          char log[log_len];
          glGetShaderInfoLog(s, log_len, nullptr, log);
          fprintf(stderr, "SHADER LOG (%s):\n%s", name.c_str(), log);
+
+         glDeleteShader(s);
+         return 0;
       }
 
       return s;
    }
 
+   GLint build_program(const string &name, GLint vs, GLint fs) {
+      GLint p = glCreateProgram();
+      glAttachShader(p, vs);
+      glAttachShader(p, fs);
+      glLinkProgram(p);
+
+      GLint stat;
+      glGetProgramiv(p, GL_LINK_STATUS, &stat);
+      if (!stat) {
+         GLint log_len;
+         glGetShaderiv(p, GL_INFO_LOG_LENGTH, &log_len);
+         char log[log_len];
+         glGetProgramInfoLog(p, log_len, nullptr, log);
+         fprintf(stderr, "SHADER LOG (%s):\n%s", name.c_str(), log);
+
+         glDeleteProgram(p);
+         return 0;
+      }
+
+      return p;
+   }
+
 public:
    void init() override {
       auto vs = build_shader(GL_VERTEX_SHADER, "vertex",
          "#version 400\n"
-         ""
          "void main(){"
-         "  int"
+         "  float x = gl_VertexID % 2;"
+         "  float y = gl_VertexID / 2;"
+         "  gl_Position = vec4(x, y, 0, 1);"
          "}");
 
       auto fs = build_shader(GL_FRAGMENT_SHADER, "fragment",
          "#version 400\n"
-         ""
          "void main(){"
-         "  int"
+         "  gl_FragColor = vec4(0, 1, 1, 0);"
          "}"
       );
 
-      program = glCreateProgram();
-      glAttachShader(program, vs);
-      glAttachShader(program, fs);
-      glLinkProgram(program);
+      program = build_program("main", vs, fs);
+
+      glGenVertexArrays(1, &vao);
    }
 
    void render() override {
+      int w, h;
+      getBounds(w, h);
+      glViewport(0, 0, w, h);
 
+      glBindVertexArray(vao);
+      glUseProgram(program);
+      glDrawArrays(GL_TRIANGLES, 0, 3);
+
+      swapbuffers();
+   }
+
+   void deinit() override {
+      glDeleteProgram(program);
+      glDeleteVertexArrays(1, &vao);
    }
 };