콘텐츠로 건너뛰기

자주 방문한 페이지

최근 방문한 페이지

navigation

Applying Projection and Camera Views

In the OpenGL ES environment, projection and camera views allow you to display drawn objects in a way that more closely resembles how you see physical objects with your eyes. This simulation of physical viewing is done with mathematical transformations of drawn object coordinates:

This lesson describes how to create a projection and camera view and apply it to shapes drawn in your GLSurfaceView.

Define a Projection

The data for a projection transformation is calculated in the onSurfaceChanged() method of your GLSurfaceView.Renderer class. The following example code takes the height and width of the GLSurfaceView and uses it to populate a projection transformation Matrix using the Matrix.frustumM() method:

// mMVPMatrix is an abbreviation for "Model View Projection Matrix"
private final float[] mMVPMatrix = new float[16];
private final float[] mProjectionMatrix = new float[16];
private final float[] mViewMatrix = new float[16];

@Override
public void onSurfaceChanged(GL10 unused, int width, int height) {
    GLES20.glViewport(0, 0, width, height);

    float ratio = (float) width / height;

    // this projection matrix is applied to object coordinates
    // in the onDrawFrame() method
    Matrix.frustumM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 3, 7);
}

This code populates a projection matrix, mProjectionMatrix which you can then combine with a camera view transformation in the onDrawFrame() method, which is shown in the next section.

Note: Just applying a projection transformation to your drawing objects typically results in a very empty display. In general, you must also apply a camera view transformation in order for anything to show up on screen.

Define a Camera View

Complete the process of transforming your drawn objects by adding a camera view transformation as part of the drawing process in your renderer. In the following example code, the camera view transformation is calculated using the Matrix.setLookAtM() method and then combined with the previously calculated projection matrix. The combined transformation matrices are then passed to the drawn shape.

@Override
public void onDrawFrame(GL10 unused) {
    ...
    // Set the camera position (View matrix)
    Matrix.setLookAtM(mViewMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f);

    // Calculate the projection and view transformation
    Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mViewMatrix, 0);

    // Draw shape
    mTriangle.draw(mMVPMatrix);
}

Apply Projection and Camera Transformations

In order to use the combined projection and camera view transformation matrix shown in the previews sections, first add a matrix variable to the vertex shader previously defined in the Triangle class:

public class Triangle {

    private final String vertexShaderCode =
        // This matrix member variable provides a hook to manipulate
        // the coordinates of the objects that use this vertex shader
        "uniform mat4 uMVPMatrix;" +
        "attribute vec4 vPosition;" +
        "void main() {" +
        // the matrix must be included as a modifier of gl_Position
        // Note that the uMVPMatrix factor *must be first* in order
        // for the matrix multiplication product to be correct.
        "  gl_Position = uMVPMatrix * vPosition;" +
        "}";

    // Use to access and set the view transformation
    private int mMVPMatrixHandle;

    ...
}

Next, modify the draw() method of your graphic objects to accept the combined transformation matrix and apply it to the shape:

public void draw(float[] mvpMatrix) { // pass in the calculated transformation matrix
    ...

    // get handle to shape's transformation matrix
    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");

    // Pass the projection and view transformation to the shader
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);

    // Draw the triangle
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);

    // Disable vertex array
    GLES20.glDisableVertexAttribArray(mPositionHandle);
}

Once you have correctly calculated and applied the projection and camera view transformations, your graphic objects are drawn in correct proportions and should look like this:

Figure 1. Triangle drawn with a projection and camera view applied.

Now that you have an application that displays your shapes in correct proportions, it's time to add motion to your shapes.

이 사이트는 쿠키를 사용하여 사이트별 언어 및 표시 옵션에 대한 환경설정을 저장합니다.

Google Play에서 성공을 거두는 데 도움이 되는 최신 Android 개발자 뉴스 및 도움말을 받아 보세요.

* 필수 입력란

완료되었습니다.

WeChat에서 Google Developers 팔로우하기

이 사이트를 (으)로 탐색할까요?

페이지를 요청했지만 이 사이트의 언어 환경설정은 입니다.

언어 환경설정을 변경하고 이 사이트를 (으)로 탐색할까요? 언어 환경설정을 나중에 변경하려면 각 페이지 하단의 언어 메뉴를 사용하세요.

이 클래스를 사용하려면 API 수준 이상이 필요합니다.

문서에 대해 선택한 API 수준이 이므로 이 문서가 표시되지 않습니다. 왼쪽 탐색 메뉴의 선택기로 문서 API 수준을 변경할 수 있습니다.

앱에 필요한 API 수준 지정에 관한 자세한 내용은 다양한 플랫폼 버전 지원을 참조하세요.

Take a short survey?
Help us improve the Android developer experience. (April 2018 — Developer Survey)