Adding backdrop

src/backdrop.cpp

@@ -0,0 +1,42 @@
+#include "backdrop.h"
+
+Backdrop::Backdrop()
+{
+    shader.addShaderFromSourceFile(QGLShader::Vertex, ":/gl/quad.vert");
+    shader.addShaderFromSourceFile(QGLShader::Fragment, ":/gl/quad.frag");
+    shader.link();
+
+    float vbuf[] = {
+        -1, -1, 0.00, 0.10, 0.15,
+        -1,  1, 0.03, 0.21, 0.26,
+         1, -1, 0.00, 0.12, 0.18,
+         1,  1, 0.06, 0.26, 0.30};
+
+    vertices.create();
+    vertices.bind();
+    vertices.allocate(vbuf, sizeof(vbuf));
+    vertices.release();
+}
+
+void Backdrop::draw()
+{
+    shader.bind();
+    vertices.bind();
+
+    const GLuint vp = shader.attributeLocation("vertex_position");
+    const GLuint vc = shader.attributeLocation("vertex_color");
+
+    glEnableVertexAttribArray(vp);
+    glEnableVertexAttribArray(vc);
+
+    glVertexAttribPointer(vp, 2, GL_FLOAT, false,
+                          5 * sizeof(GLfloat), 0);
+    glVertexAttribPointer(vc, 3, GL_FLOAT, false,
+                          5 * sizeof(GLfloat),
+                          (GLvoid*)(2 * sizeof(GLfloat)));
+
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 8);
+
+    vertices.release();
+    shader.release();
+}