Android OpenGL ES – Part 6: Camera View

1. Reset the pyramid position

Open the main.cpp file.
Modify the Java_dev_anastasioscho_glestriangle_NativeLibrary_nOnDrawFrame function as follows:

/* code */

glm::mat4 model = glm::mat4(1.0f);
model = glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));
model = glm::rotate(model, glm::radians(currentAngle), glm::vec3(0.0f, 1.0f, 0.0f));

/* code */

2. Remove the rotation animation

Delete the following line of code from Java_dev_anastasioscho_glestriangle_NativeLibrary_nOnDrawFrame:

model = glm::rotate(model, glm::radians(currentAngle), glm::vec3(0.0f, 1.0f, 0.0f));

3. Modify the vertex shader

Modify the vertex shader source code as follows:

/* code */

static const GLchar vertexShaderSource[] =
   "#version 310 es\n"
   "layout (location = 0) in vec3 pos;\n"
   "out vec4 vColor;\n"
   "uniform mat4 model;\n"
   "uniform mat4 projection;\n"
   "uniform mat4 view;\n"
   "void main()\n"
   "{\n"
   "gl_Position = projection * view * model * vec4(pos, 1.0);\n"
   "vColor = vec4(clamp(pos, 0.0, 1.0), 1.0);\n"
   "}\n";

/* code */

4. Set the uniform variable

Declare the following global variable:

/* code */

GLuint program, triangleVAO, triangleVBO, triangleIBO;
GLint uniformModel, uniformProjection, uniformView;
glm::mat4 projectionMatrix;

/* code */

Modify the createProgram function as follows:

/* code */

uniformModel = glGetUniformLocation(program, "model");
uniformProjection = glGetUniformLocation(program, "projection");
uniformView = glGetUniformLocation(program, "view");

return;

/* code */

Modify the Java_dev_anastasioscho_glestriangle_NativeLibrary_nOnSurfaceChanged function as follows:

/* code */

glUniformMatrix4fv(uniformProjection, 1, GL_FALSE, glm::value_ptr(projectionMatrix));

glm::vec3 cameraPosition = glm::vec3(0.0f, 0.0f, 2.5f);
glm::vec3 cameraTarget = glm::vec3(0.0f, 0.0f, 0.0f);
glm::vec3 worldUp = glm::vec3(0.0f, 1.0f, 0.0f);

glm::mat4 viewMatrix = glm::lookAt(cameraPosition, cameraTarget, worldUp);
glUniformMatrix4fv(uniformView, 1, GL_FALSE, glm::value_ptr(viewMatrix));

glBindVertexArray(triangleVAO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, triangleIBO);

/* code */

Note

cameraTarget is the position of the object the camera is looking at (in this case the pyramid).

worldUp is a vector pointing upwards at the world (for example this could be the sky in our world).

5. Move the camera around the pyramid

Modify the Java_dev_anastasioscho_glestriangle_NativeLibrary_nOnSurfaceChanged function as follows:

/* code */

glUniformMatrix4fv(uniformModel, 1, GL_FALSE, glm::value_ptr(model));
glUniformMatrix4fv(uniformProjection, 1, GL_FALSE, glm::value_ptr(projectionMatrix));

float camX = sin(glm::radians(currentAngle)) * 2.5f;
float camZ = cos(glm::radians(currentAngle)) * 2.5f;

glm::vec3 cameraPosition = glm::vec3(camX, 0.0f, camZ);
glm::vec3 cameraTarget = glm::vec3(0.0f, 0.0f, 0.0f);

/* code */

6. References

https://learnopengl.com/Getting-started/Camera