egl: match geometry position of glxgears

There's two things that differs about the geometry position of this port
of glxgears:

1. The camera is moved back by the wrong amount.
2. The projection matrix is computed the wrong way.

So let's remedy this, and make the rendering closer to the original.

Reviewed-by: Adam Jackson <ajax@redhat.com>

1 files changed, 21 insertions, 22 deletions

diff --git a/src/egl/opengles2/es2gears.c b/src/egl/opengles2/es2gears.c
index 37fb6a41..39dc9a20 100644
--- a/src/egl/opengles2/es2gears.c
+++ b/src/egl/opengles2/es2gears.c
@@ -408,35 +408,33 @@ invert(GLfloat *m)
 }
 
 /** 
- * Calculate a perspective projection transformation.
+ * Calculate a frustum projection transformation.
  * 
  * @param m the matrix to save the transformation in
- * @param fovy the field of view in the y direction
- * @param aspect the view aspect ratio
- * @param zNear the near clipping plane
- * @param zFar the far clipping plane
+ * @param l the left plane distance
+ * @param r the right plane distance
+ * @param b the bottom plane distance
+ * @param t the top plane distance
+ * @param n the near plane distance
+ * @param f the far plane distance
  */
-void perspective(GLfloat *m, GLfloat fovy, GLfloat aspect, GLfloat zNear, GLfloat zFar)
+static void
+frustum(GLfloat *m, GLfloat l, GLfloat r, GLfloat b, GLfloat t, GLfloat n, GLfloat f)
 {
    GLfloat tmp[16];
    identity(tmp);
 
-   double sine, cosine, cotangent, deltaZ;
-   GLfloat radians = fovy / 2 * M_PI / 180;
-
-   deltaZ = zFar - zNear;
-   sincos(radians, &sine, &cosine);
-
-   if ((deltaZ == 0) || (sine == 0) || (aspect == 0))
-      return;
-
-   cotangent = cosine / sine;
+   GLfloat deltaX = r - l;
+   GLfloat deltaY = t - b;
+   GLfloat deltaZ = f - n;
 
-   tmp[0] = cotangent / aspect;
-   tmp[5] = cotangent;
-   tmp[10] = -(zFar + zNear) / deltaZ;
+   tmp[0] = (2 * n) / deltaX;
+   tmp[5] = (2 * n) / deltaY;
+   tmp[8] = (r + l) / deltaX;
+   tmp[9] = (t + b) / deltaY;
+   tmp[10] = -(f + n) / deltaZ;
    tmp[11] = -1;
-   tmp[14] = -2 * zNear * zFar / deltaZ;
+   tmp[14] = -(2 * f * n) / deltaZ;
    tmp[15] = 0;
 
    memcpy(m, tmp, sizeof(tmp));
@@ -523,7 +521,7 @@ gears_draw(void)
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
    /* Translate and rotate the view */
-   translate(transform, 0, 0, -20);
+   translate(transform, 0, 0, -40);
    rotate(transform, 2 * M_PI * view_rot[0] / 360.0, 1, 0, 0);
    rotate(transform, 2 * M_PI * view_rot[1] / 360.0, 0, 1, 0);
    rotate(transform, 2 * M_PI * view_rot[2] / 360.0, 0, 0, 1);
@@ -544,7 +542,8 @@ static void
 gears_reshape(int width, int height)
 {
    /* Update the projection matrix */
-   perspective(ProjectionMatrix, 60.0, width / (float)height, 1.0, 1024.0);
+   GLfloat h = (GLfloat)height / (GLfloat)width;
+   frustum(ProjectionMatrix, -1.0, 1.0, -h, h, 5.0, 60.0);
 
    /* Set the viewport */
    glViewport(0, 0, (GLint) width, (GLint) height);