diff --git a/samplecode/SampleTestGL.cpp b/samplecode/SampleTestGL.cpp
index 210d779..04e47b6 100644
--- a/samplecode/SampleTestGL.cpp
+++ b/samplecode/SampleTestGL.cpp
@@ -9,6 +9,164 @@
 #include "SkShader.h"
 #include "SkUtils.h"
 
+#include <AGL/agl.h>
+#include <OpenGL/gl.h>
+
+static void test_draw_gl(SkCanvas* canvas) {
+    const float verts[] = {
+        10, 10, 250, 250, 490, 10
+    };
+    const float texs[] = {
+        0, 0, 0.5f, 0, 1, 1
+    };
+    const uint8_t colors[] = {
+        0, 0, 0, 1,
+        128, 0, 0, 1,
+        255, 255, 0, 1
+    };
+    
+    glEnableClientState(GL_VERTEX_ARRAY);
+    glVertexPointer(2, GL_FLOAT, 0, verts);
+
+    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
+//    glTexCoordPointer(2, GL_FLOAT, 0, texs);
+
+    glEnableClientState(GL_COLOR_ARRAY);
+    glColorPointer(4, GL_UNSIGNED_BYTE, 0, colors);
+
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+}
+
+static const char* gVertShaderText =
+    "varying vec2 uv;"
+    "void main(void) {"
+    "    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;"
+    "    uv = vec2(gl_Color);"
+    "}";
+
+static const char* gFragShaderText =
+    "varying vec2 uv;"
+    "void main(void) {"
+    "    float u = uv.x;"
+    "    float v = uv.y;"
+    "    if (u*u > v) {"
+"    gl_FragColor = vec4(1.0, 0, 0, 1.0);"
+    "    } else {"
+    "    gl_FragColor = vec4(0, 1.0, 0, 1.0);"
+    "}"
+    "}";
+
+static bool compile_shader(GLuint shader) {
+    glCompileShader(shader);
+
+    GLint success;
+    glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
+    if (!success) {
+        GLchar buffer[256];
+        glGetShaderInfoLog(shader, sizeof(buffer), NULL, buffer);
+        SkDebugf("---- glCompileShader failed: %s\n", buffer);
+        return false;
+    }
+    return true;
+}
+
+static bool link_program(GLuint program) {
+    glLinkProgram(program);
+    GLint success;
+    glGetProgramiv(program, GL_LINK_STATUS, &success);
+    if (!success) {
+        GLchar buffer[256];
+        glGetProgramInfoLog(program, sizeof(buffer), NULL, buffer);
+        SkDebugf("---- glLinkProgram failed: %s\n", buffer);
+        return false;
+    }
+    return true;
+}
+
+static void test_glshader(SkCanvas* canvas) {
+    GLuint vertShader = glCreateShader(GL_VERTEX_SHADER);
+    GLuint fragShader = glCreateShader(GL_FRAGMENT_SHADER);
+
+    glShaderSource(vertShader, 1, &gVertShaderText, NULL);
+    glShaderSource(fragShader, 1, &gFragShaderText, NULL);
+
+    if (!compile_shader(vertShader)) { return; }
+    if (!compile_shader(fragShader)) { return; }
+
+    GLuint program = glCreateProgram();
+    glAttachShader(program, vertShader);
+    glAttachShader(program, fragShader);
+    if (link_program(program)) {
+        glUseProgram(program);
+        test_draw_gl(canvas);
+        glUseProgram(0);
+    }
+    glDeleteProgram(program);
+    glDeleteShader(vertShader);
+    glDeleteShader(fragShader);
+}
+
+static void setmatrix6(SkMatrix* matrix, const float val[]) {
+    matrix->reset();
+    for (int i = 0; i < 6; i++) {
+        matrix->set(i, val[i]);
+    }
+}
+
+static void testinvert() {
+    SkMatrix matrix;
+
+    const float vals[] = { 0,9,.000001,10000,0,0 };
+    setmatrix6(&matrix, vals);
+
+    const float vals2[] = { 0,100,71,9,0,7 };
+    SkMatrix tmp;
+    setmatrix6(&tmp, vals2);
+    
+    matrix.preConcat(tmp);
+    matrix.dump();
+
+    SkMatrix inverse;
+    matrix.invert(&inverse);
+    inverse.dump();
+    
+    matrix.preConcat(inverse);
+    matrix.dump();
+
+//    o2dContext.setTransform(0,9,.000001,10000,0,0);
+//    o2dContext.transform(0,100,71,9,0,7);
+//    o2dContext.setTransform(0,6,95,4,1,0);
+}
+
+/*
+ [0]	9.9999997e-005	float
+ [1]	9.0000003e-006	float
+ [2]	7.0000001e-006	float
+ [3]	1000000.0	float
+ [4]	90639.000	float
+ [5]	70000.000	float
+ [6]	0.00000000	float
+ [7]	0.00000000	float
+ [8]	1.0000000	float
+ */
+static void testinvert2() {
+    const float val[] = {
+        9.9999997e-005, 9.0000003e-006, 7.0000001e-006,
+        1000000.0, 90639.000, 70000.000
+    };
+    SkMatrix matrix;
+    setmatrix6(&matrix, val);
+    matrix.dump();
+
+    SkMatrix inverse;
+    matrix.invert(&inverse);
+    inverse.dump();
+
+    matrix.preConcat(inverse);
+    matrix.dump();
+    // result is that matrix[3] is 49550 instead of 0 :(
+}
+
 static void show_ramp(SkCanvas* canvas, const SkRect& r) {
     SkPoint pts[] = { r.fLeft, 0, r.fRight, 0 };
     SkColor colors[] = { SK_ColorRED, SK_ColorBLUE };
@@ -25,6 +183,7 @@
 class TestGLView : public SkView {
 public:
 	TestGLView() {
+        testinvert2();
     }
     
 protected:
@@ -44,6 +203,9 @@
     virtual void onDraw(SkCanvas* canvas) {
         drawBG(canvas);
         
+        test_glshader(canvas);
+        return;
+        
         SkRect r;
         r.set(0, 0, 100, 100);