shaders: initialize vertexes once

Create a buffer for the vertex data and place vertexes
there at initialization time.  Then just use the buffer
for each texture blit.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

include/ui/shader.h

@@ -3,7 +3,9 @@
 
 #include <epoxy/gl.h>
 
-void qemu_gl_run_texture_blit(GLint texture_blit_prog);
+GLuint qemu_gl_init_texture_blit(GLint texture_blit_prog);
+void qemu_gl_run_texture_blit(GLint texture_blit_prog,
+                              GLint texture_blit_vao);
 
 GLuint qemu_gl_create_compile_shader(GLenum type, const GLchar *src);
 GLuint qemu_gl_create_link_program(GLuint vert, GLuint frag);

ui/console-gl.c

@@ -33,6 +33,7 @@
 
 struct ConsoleGLState {
     GLint texture_blit_prog;
+    GLint texture_blit_vao;
 };
 
 /* ---------------------------------------------------------------------- */
@@ -47,6 +48,9 @@ ConsoleGLState *console_gl_init_context(void)
         exit(1);
     }
 
+    gls->texture_blit_vao =
+        qemu_gl_init_texture_blit(gls->texture_blit_prog);
+
     return gls;
 }
 
@@ -131,7 +135,8 @@ void surface_gl_render_texture(ConsoleGLState *gls,
     glClearColor(0.1f, 0.1f, 0.1f, 0.0f);
     glClear(GL_COLOR_BUFFER_BIT);
 
-    qemu_gl_run_texture_blit(gls->texture_blit_prog);
+    qemu_gl_run_texture_blit(gls->texture_blit_prog,
+                             gls->texture_blit_vao);
 }
 
 void surface_gl_destroy_texture(ConsoleGLState *gls,

ui/shader.c

@@ -29,21 +29,42 @@
 
 /* ---------------------------------------------------------------------- */
 
-void qemu_gl_run_texture_blit(GLint texture_blit_prog)
+GLuint qemu_gl_init_texture_blit(GLint texture_blit_prog)
 {
-    GLfloat in_position[] = {
+    static const GLfloat in_position[] = {
         -1, -1,
         1,  -1,
         -1,  1,
         1,   1,
     };
     GLint l_position;
+    GLuint vao, buffer;
+
+    glGenVertexArrays(1, &vao);
+    glBindVertexArray(vao);
+
+    /* this is the VBO that holds the vertex data */
+    glGenBuffers(1, &buffer);
+    glBindBuffer(GL_ARRAY_BUFFER, buffer);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(in_position), in_position,
+                 GL_STATIC_DRAW);
 
-    glUseProgram(texture_blit_prog);
     l_position = glGetAttribLocation(texture_blit_prog, "in_position");
-    glVertexAttribPointer(l_position, 2, GL_FLOAT, GL_FALSE, 0, in_position);
+    glVertexAttribPointer(l_position, 2, GL_FLOAT, GL_FALSE, 0, 0);
     glEnableVertexAttribArray(l_position);
-    glDrawArrays(GL_TRIANGLE_STRIP, l_position, 4);
+
+    glBindBuffer(GL_ARRAY_BUFFER, 0);
+    glBindVertexArray(0);
+
+    return vao;
+}
+
+void qemu_gl_run_texture_blit(GLint texture_blit_prog,
+                              GLint texture_blit_vao)
+{
+    glUseProgram(texture_blit_prog);
+    glBindVertexArray(texture_blit_vao);
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 }
 
 /* ---------------------------------------------------------------------- */