I am able to draw a rectangle in android openGL using
private float vertices[] = {
-1.0f, 0.8f, 0.0f, // V1 - bottom left
-1.0f, 1.0f, 0.0f, // V2 - top left
1.0f, 0.8f, 0.0f, // V3 - bottom right
1.0f, 1.0f, 0.0f // V4 - top right
};
But i want to give vertices based on user Touch using event.getX() and event.getY(). Those values seem to make the rectangle go out of the screen.
How do i see that the rectangle is drawn where the user touches?
Related
I'm new to image and video manipulation on Android and have a scenario where I'd like to load a video file (.mp4) into my app and programmtically modify it such that each frame in the video is horizontally flipped (mirrored). The video should be unchanged otherwise. One constraint is that I cannot use any third-party frameworks, so this needs to be done using the Android SDK only, if possible.
Is this possible, and if so, how should I do this? I came across the MediaCodec class, but I haven't found any solid examples illustrating how to use this class.
https://android.googlesource.com/platform/cts/+/jb-mr2-release/tests/tests/media/src/android/media/cts/ExtractDecodeEditEncodeMuxTest.java There is file TextureRender.java you need change matrix U-V and you can flip, rotate.
private final float[] mTriangleVerticesData = {
// X, Y, Z, U, V
-1.0f, -1.0f, 0, 1.f, 0.f,
1.0f, -1.0f, 0, 0.f, 0.f,
-1.0f, 1.0f, 0, 1.f, 1.f,
1.0f, 1.0f, 0, 0.f, 1.f,
};
It works like this (just ignore small texture).
Just experiment with U-V coordinates.
I read that OpenGL have origin in bottom-left corner, but the screen for touch have the origin in top-left corner.
So, can I set
gl.glOrthof(0.0f, this.width, this.height, 0.0f, 1.0f, -1.0f);
to match OpenGL to screen coordinates?
Will I have difficulties with this way?
I have a texture that I can render in OpenGL-ES with an orthogonal identity matrix:
gst_gl_shader_set_uniform_matrix_4fv(shader, "u_transformation", 1, FALSE, identity_matrix);
I want to move "the pixels around": half of the top is going to the left, half of the bottom is going to the right as shown on the image below. Is there an "easy" way to do that? I'm on Android.
On this related answered question How to crop/clip in OpenGL using u_transformation, I was able to keep the top part 'a' or the bottom part 'e'. Would there be a way to do a "double gst_gl_shader_set_uniform_matrix_4fv" after "cutting" the scene in two?
The transformation that you want here cannot be represented by a transformation matrix. Matrices can only represent certain classes of transformations. In 3D space:
A 3x3 matrix represents a linear transformation. Typical examples include rotation, scaling, mirroring, shearing.
A 4x3 matrix represents an affine transformation. On top of the above, this includes translations.
If you extend the 3D space to homogenous coordinates with 4 components, a 4x4 matrix can represent additional classes of transformations, like projections.
The transformation in your sketch is none of the above. So applying a matrix to your vertices will not be able to do this.
So what can you do? Two options come to mind:
If you can easily draw the two parts (top/bottom, left/right) separately, you can obviously do that, and simply change the transformation between rendering the two parts.
Apply the logic in your shader code.
For option 2, you could do this either in the vertex or fragment shader. If you have no primitives that cross the boundary between the two parts, handling it in the vertex shader would be more efficient. Otherwise, similar logic can be used in the fragment shader.
Sketching the critical parts for the vertex shader case, let's say you currently have the following that gives you the arrangement in the left side of your sketch:
// Calculate output position and store it in variable "pos".
gl_Position = pos;
To get the second arrangement, the logic could look like this (completely untested...):
if (pos.y > 0.0) {
gl_Position = vec4(0.5 * pos.x - 0.5, 2.0 * pos.y - 1.0, pos.zw)
} else {
gl_Position = vec4(0.5 * pos.x + 0.5, 2.0 * pos.y + 1.0, pos.zw);
}
The idea is that you check whether the vertex is in the top or bottom half, and scale/shift it accordingly to map the top half of the coordinate space into the left half, and the bottom half of the coordinate space into the right half.
This could be streamlined some more by replacing the conditional with a sign operation:
float s = sign(pos.y);
gl_Position = vec4(0.5 * pos.x - sign * 0.5, 2.0 * pos.y - sign, pos.zw);
Some more care will be needed if pos.w is not 1.0, which happens if you e.g. applied a perspective projection to your vertices. In that case, you'll have to incorporate the division by w in the calculations above.
The formula described in Reto answers 'semi' work as they only produce the "a" on the left or the "e" on the right but not both at the same time.
The solution I found is to double the number of vertices and indices and play around with the vertices coordinates like this:
static const GLfloat vertices[] = {
1.0f, 1.0f, 0.0f, 1.0f, 0.0f,
0.0f, 1.0f, 0.0f, 0.0f, 0.0f,
0.0f, -1.0f, 0.0f, 0.0f, 0.5f,
1.0f, -1.0f, 0.0f, 1.0f, 0.5f,
0.0f, 1.0f, 0.0f, 1.0f, 0.5f,
-1.0f, 1.0f, 0.0f, 0.0f, 0.5f,
-1.0f, -1.0f, 0.0f, 0.0f, 1.0f,
0.0f, -1.0f, 0.0f, 1.0f, 1.0f
};
static const GLushort indices[] = { 0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7 };
i am following nehe's tutorials.
i intent to make a menu or at least buttons with opengl, yet object overlap on the menu
my code on the drawFrame function in the renderer
gl.glLoadIdentity();
gl.glScalef(0.05f, 0.05f, 0.05f);
gl.glTranslatef(0.0f, 0.0f, z-zKonum);
gl.glRotatef(xAcisi, 1.0f, 0.0f, 0.0f);
gl.glRotatef(yAcisi, 0.0f, 1.0f, 0.0f);
dokukup.ciz(gl);
gl.glLoadIdentity();
gl.glTranslatef(3.6f, -1.5f, z);
tusYukari.ciz(gl);
gl.glLoadIdentity();
gl.glTranslatef(2.5f, -1.5f, z);
tusAsagi.ciz(gl);
how do i get my menu buttons dominant(always on the top) on the overlapping?
You can get the buttons to appear always on top by drawing the buttons last and disabling depth testing when drawing the buttons. Then make sure to enable depth testing again before drawing the next frame so that your 3D geometry renders properly.
In your drawFrame function you would do the following steps:
Enable depth testing
Draw the main scene geometry
Disable depth testing
Draw the buttons
I want to draw opengl texture at full screen.
(texture : 128x128 ===> device screen : 320x480)
Below code works good, but texture is small.
I have to use only glFrustumf function(not glOrthof function).
How can I draw texture in full screen size?
// this is android source code
float ratio = (float) screenWidth / screenHeight;
gl.glMatrixMode(GL10.GL_PROJECTION);
gl.glLoadIdentity();
gl.glFrustumf(-ratio, ratio, -1, 1, 1, 10);
GLU.gluLookAt(gl, 0.0f, 0.0f, -2.5f, // eye
0.0f, 0.0f, 0.0f, // center
0.0f, 1.0f, 0.0f); // up
// draw blah blah
Why do you have to use glFrustum only? Switching to glOrtho for drawing the background, then switching to glFrustum for regular drawing would be the canonical solution.
BTW: gluLookAt must happen in the modelview matrix, not in the projection matrix like you do right now. As it stands your code is broken and if you were a student in one of my OpenGL classes I'd give you negative points for this cardinal error.